Mineral Collections

The Golden Age of Mineral Collecting: Today is better than ever!

It was the best of times, it was the worst of times, it was the age of wisdom, it was the age of foolishness, it was the epoch of belief, it was the epoch of incredulity, it was the season of light, it was the season of darkness, it was the spring of hope, it was the winter of despair, Charles Dickens, in A Tale of Two Cities (1859).

Mineral Collecting has evolved tremendously in the last 65 years. Many collectors bemoan the passing of the “golden age” when spectacular mineral specimens were available for purchase. However, in terms of “classics”today is the true golden age (all thumbnail figures can be clicked for full-sized images).

In 1798 Thomas Malthus published his An Essay on the Principle of Population and postulated that catastrophe for mankind was inevitable because population growth is exponential and life essential resources (such as food and water) tended to only grow arithmetically. This simple essay gave rise to a school of gloom and doom, Malthusianism, that has been applied to everything from oil production to luxury items; basically, in a world of fast growing population the demand for commodities will eventually outstrip the supply, and the scarcity of the resources will lead to conflict and ultimately a decimation of demand. However, in the two centuries since Malthus first pinned his thoughts on the clash between supply and demand, the concept of “catastrophe” has been mostly avoided because the same demand that made resources scarce spurred unimaginable creativity and innovation. Between 1800 and the start of the new millennium the world’s population increased 6 fold, yet agriculture increased 10 fold! Many more people, and even more food – and the supply vs demand dynamic was tipped on it’s head.

Malthusianism — population and demand grows exponentially, while supply of resources increases arithmetically. When demand exceeds supply new dynamics happen – perhaps disaster, or perhaps innovation.

It seems a bizarre reach, and perhaps even a non-sequitur, to reference Malthusian theory in a discussion of the “golden age” of mineral collecting. However, the parallels with “peak oil” predictions and the demise of the modern mineral production of truly fine specimens are surprising. Since 1980 the number of significant mineral specimens discoveries is extraordinary; Bunker Hill pyromorphite, Sweet Home rhodochrosite, Red Cloud wulfenite, Milpillas azurite (and other secondary copper minerals), Fresnillo stephanite, Merelan tanzanite and the incredible gemstone minerals from Pakistan along with the flood of minerals from China. Never before has the quantity of high quality minerals been remotely like it is today.

Aquamarine from Pakistan recovered in the last 10 years – the quality is unrivaled in history.

There are many reasons why Malthusian thinking has failed in predicting the dynamics of the mineral collecting hobby, but mostly it is a change in what economists call the demand relationship. Although there has always been a supply-demand relationship in mineral collecting, the foundations for that relationship changed as high-end mineral specimens became “works of art”. University of Chicago economist David Galenson likes to use the career arc of impressionist Paul Cézanne as an exemplar for the art market. In 1895 Cézanne had his first one-man show in Paris, and sold a single painting for 400 francs. A painting that did not sell in this show was later bought in 1899 for 4,400 francs – a tenfold increase in 4 years! In 1913 a Cézanne work sold for 25,000 francs, and in 1925 a painting was sold in auction for 528,000 francs. What changed in those 30 years? Certainly not Cézanne — he died in 1906. Some might argue that Cézanne’s work was simply unappreciated when first viewed, but a more nuanced analysis suggests that a very small number of art collectors were influenced by an even smaller number of art dealers to view the painter’s work as an absolute essential “to have”. Passion – probably influenced by dealer manipulation – drove fierce competition.

The mineral collecting hobby now has the same drivers as fine art. There are many rumors of individual mineral specimens that sell for several million dollars; “I could have bought that azurite for 100 dollars 10 years ago” it has become an old saw for long-time collectors. There is a community longing for years past when a collector of modest means could build a fabulous ensemble of minerals. There is a malaise that a “golden age” has passed, and mineral collecting is in a death spiral. However, the very fact that there is a “minerals are art” market is probably why there are more how quality specimens than ever for sale. This truly is the golden age of mineral collecting.

The Tucson Gem and Mineral Show began in 1955, and help span a “golden age” of mineral collecting that orbited around mineral clubs and annual shows. The TGMS show was in the quonset hut pictured above between 1955-1971. Humble beginning for a show that now has special exhibits and displays that are valued at 100 million dollars or more.

The First Golden Age: The Rock Hounding 50s and 60s

Mineral collecting – as a hobby, profession, scientific endeavor – has been around for at least 500 years. Wendell Wilson wrote a fabulous tome on the origins of collecting, The History of Mineral Collecting, 1530-1799 in 1994. “Collecting” coincided with the rise of science applied to mining, and Georgics Agricola’s De Natura Fossilium published in 1546 is considered the first modern textbook of mineralogy. Although there are some exceptions, the first 350 years of mineral collecting was dominated by the gentleman naturalist, and specimen quality was not as important as documenting topographic mineralogy. By the end of the 19th century there were scores of serious mineral collectors in the US (and even more in Europe) – mostly rich business men — and minerals dealers became a real profession. However, in the US the most important event in the later half of the 19th century that changed mineral collecting was the rise of high education. Hundreds of universities and colleges sprung up across the nation, and geology was taught in nearly all; remarkably, all these new colleges sought to acquire geology collections, including minerals. In response to demand, companies like Ward’s (Ward’s Natural Science was founded in 1862 by Henry A. Ward) mass marketed minerals, and the “common man” could own specimens from around the world. This spawned mineral clubs – The New York Mineralogical Club was founded in 1886, the Philadelphia Mineralogical Society in 1892, and by 1900 there were at least 2 dozen amateur groups promoting mineralogy. These societies had a tremendous impact on a generation of scientists; one of my favorite stories is the connection between Linus Pauling and J. Robert Oppenheimer (all stories come back to Los Alamos…..) – they were both mineral collectors! In fact, Oppenheimer gave a several hundred specimens to Pauling when he was at Caltech, and in turn, Pauling gave many of these to his son-in-law, Barclay Kamb, who later became the head of the Earth and Planetary Sciences department at Caltech (he was the department head when I was a student there in the 1970s).

Quartz crystals originally in the Oppenheimer Collection that were given to Luis Pauling. Photograph by Anna Wilsey.

By the late 1930s there were at least 120 clubs in the US, and “rock hounding” was a popular past time. However, it was with the end of World War II that saw an explosion in rock hounding; the hobby literally swept across the country, and by 1947 there were at least a thousand clubs. The American Federation of Mineralogical Societies (AMFS) was founded in 1947, and club gem and mineral shows became common place. One of the most influential of these clubs was the Tucson Gem and Mineral Society (TGMS) which was founded in 1946. Tucson was an international center for mineral exploration, and the University of Arizona had strong academic programs in economic geology and mining engineering. There were more than a 1000 mines – active or abandon – within 100 miles of Tucson, and this was a collectors paradise (anecdotally, when I graduated from Caltech I chose to take a position at the University of Arizona based on this “center of the mineral universe” – it certainly was not the center of theoretical and computational geophysics). In 1955 TGMS launched its annual show (nine dealers, but more than 1500 attendees!). Soon the TGMS show aggressively moved to the national stage – and attracted exhibits from museums like the Smithsonian Institution – and by the mid-1960s was attracting an international cliental. The 1970 were halcyon days for mineral collecting – thousands of colorful minerals were pouring out of Mexico, and the TGMS show was a perfect market place. This is what most collectors think of as the “golden age”. One of the factors that contributes to the nostalgia was the modest prices charged for minerals – it was a mom and pop enterprise catering to a broad spectrum of collectors.

The TGMS show changed the mineral collecting hobby – it became big business. Satellite shows proliferated, including the hotel room collection of dealers that set up at the Desert Inn. This was the front end to the transformation of mineral collecting as a populist hobby to high art.

The dramatic growth the mineral collecting enterprise naturally became stratified. The “best” minerals, especially those that were colorful, became much more expensive. In addition, the concept of a market for minerals that paralleled the market for art pushed this segregation even further. By the late 1970s there were mineral dealers in the TGMS show that only “dealt” with high end material; these dealers would sell individual specimens for more money that most of the mom and pop dealers would make during the entire TGMS show. It was the Malthusian end – demand crushed the supply side of the equation. Further, it seemed advances in mechanized mining, solution extraction, and exploration of low grade ores meant that the flow of collectable minerals was slowing to a trickle.

Much grumbling was heard in the late 1970s that the mineral collecting hobby was “over”. Purchasing high quality specimens was becoming out of reach for many collectors, and large number of the collecting localities in the US were being reclaimed or closed to the causal rock hound. However, the very driver that caused this grumbling – money – was allowing collecting to be done on a commercial scale. Collecting contracts were profitable in some large active mines, and the potential to realize profits began to entice wealthy collectors to invest in specialty mining: the Sweet Home Mine rhodochrosite and Red Cloud wulfenite mining endeavors would not have happened without a market for million dollar rocks. In the mid-1990s dealers began to market on the internet – it was an innovative way to reach remote customers, but it also had the remarkable effect of democratizing the pricing of minerals. Miners in Bolivia could actually see how much a dealer in the US was asking for the vivianite specimen the miner had sold to the dealer a month ago. A new supply-demand relationship in mineral collecting was born.

Silver in friable quartz, Andaychagua Mine, Peru (photograph by Jeff Scovil). The specimen is 5.2 cm tall, and shows a plate of spinel twins; mined in May, 2015.

Today’s Golden Age – At Least for Silver Minerals

There is no question that the mineral collecting hobby in 2016 is very different than it was in the 1970s. However, the quality of minerals being bought and sold today is higher than ever. The market model is excluding young collectors, and restricting collectors of modest means (I often hear about “bargains” to be found for the modest collector – however, when every display at a mineral show is filled with specimens that costs thousands of dollars, the collector of modest means is psychologically disposed to simply walk away). But, for collectors that can afford to invest, the minerals that are available today are exceptional. This is especially true for colorful or gem minerals – but is also true for the “ugly” dark minerals, like silver minerals!

An exemplar for this new golden age are a few personal additions to my collection in the last 24 months – all specimens that were mined or recovered during in past few years. I am a collector of modest means, but I have also been collecting minerals for nearly 55 years. That long tenure means that I have many more avenues to acquiring minerals that beginners, or even most collectors, have at their disposal. These examples are not “trophies”, but are still among the best known for the species.

During the summer of 2015 a few dozen acanthite specimens with specular luster were recovered along the Veta Madre of Guanajuato. The Guanajuato mines are arguably the most famous silver locality in the world, and certainly the source of the “best” classic acanthites — strings of stacked pseudo cubes. This recent find is different, but still spectacular, from the classics.

Complex cluster of acanthite crystals, 3.2 cm high from the Mina La Cata, Guanajuato, GTO, Mexico (Jeff Scovil, photograph).

Guanajuato is located 475 km northwest of Mexico City, along the “silver channel” a string of incredible silver districts running along the spine of Mexico. In 1548, a group of ore haulers was returning to the recently discovered silver camp of Zacatecas after delivering their load to Mexico City. The haulers decided to camp beneath a rock outcrop that resembled a frog – the name Guanajuato is said to be a Spanish pronunciation of the Tarascan Indian word for hill of frogs (Martin, 1906). A little prospecting uncovered a vein of silver, and a claim was staked on one of the world’s greatest mining camps. Over then next 475 years Guanajuato would go through periods of boom and bust; the booms were extraordinary! In the 18^th century Guanajuato accounted for two thirds of the world’s total silver production. In 1906, Englishman Percy Martin wrote a promotional book call Mexico’s Treasure House (Guanajuato), in which he extolled the virtues of the silver district: “The silver mines of Guanajuato differ from most other mines in the world inasmuch as there is nothing conjectural nor problematic about them”. Hardly true, but there is nothing conjectural about the fact that for 450 years the district has supplied unsurpassed mineral specimens.

Basic geologic map of Guanajuato from Wendke, 1965. The Mina La Cata is located between the Valencia and Mellado.

During the summer of 2014, and again in the spring of 2015, very fine spinel twinned silvers were found at the Andaychagua Mine, in the San Cristobal District of Peru. The San Cristobal District has long been known for silver minerals, but the new find are the best herring bone silvers to be mined since the Batopilas, Mexico silvers recovered in the 1980s.

Multiple plates of spinel twinned silver from the Andaychagua Mine Peru. The specimen is nine cm tall. Jeff Scovil photograph.

The San Cristobal District is located in the Cordillera Occidental about 120 km east of Peru and the first mines in this region were recorded in the 16th century. The region has a rich history of producing silver-bearing mineral specimens and some fine spinel twins of native silver (from the San Cristobal Mine) in a crumbly siderite matrix were on the market in the mid-1980s. The Andaychagua mine is one of four (the other three being the San Cristobal, Ticlio and Carahuacra) in the district that are active, and is presently owned by Volcan Compañía Minera S.A. (acquired in 1997). The annual silver production from the district is about 250,000 kg – however, specimens for collectors have been rare for the last 20 years.

Location of the major mining districts in Peru. San Cristobal is a mountainous district with an average elevation of approximately 14,500′ (map from Bartlet, 1984).

The Machacamarca District, also known as the Colavi District, is located in the Bolivian tin belt, a chain of related mineral deposits that extends nearly 1000 km north-to-south along the eastern Cordillera of Bolivia. The northern part of the belt is marked by Suko, and the southern end is Pirquitas in Argentina. The world’s most famous silver deposit – Cerro Rico in Potosi – sits in the middle of the tin belt. Colavi is only a few 10s km north of Cerro Rico – but those few km are across the most rugged mountainous terrain in the world.

The mine of the Bolivian Tin Belt. In the center is Potosi, home of Cerro Rico. Machacamarca, Colavi is located due north of Potosi.

In April of 2015 a significant find of freibergite crystals were recovered from an obscure mine identified as the Melgarejo Mine. Numerous geologists that work in the area scoff at the locality – they don’t doubt Colavi, but have never heard of nor seen the Melgarejo Mine. Mariano Melgarejo is a Bolivian historical figure of some considerable ill repute – he give a significant portion of eastern Bolivia to Brazil in the Treaty of Ayacucho in exchange for a magnificent white horse, and in 1870 ordered his troops to march to Paris to protect France from an invading Germany. Nevertheless, the freibergite crystals are certainly the largest ever found. It is difficult to tell the difference between friebergite and tetrahedrite (that carries some amount of silver), and many specimens labeled freibergite turn out to be the much more common tetrahedrite. The specimen shown below is the one of the very best found, and I personally checked the structure to confirm its identification. Considering that freibergite has been identified from hundreds of localities since the late 18th century, the fact that “world’s best” now appear is remarkable.

Freibergite crystals, 7.2 cm across (Jeff Scovil photograph). The reputed locality is the Melgarejo Mine, Machacamarca, Colvai, Bolivia. “Reputed” because some have questioned whether the actual locality was obscured to preserve a source.

The Imiter deposit is located in the Anti-Atlas Mountains, Morocco, northern Africa, and it is one of the largest silver deposits in the world. Imiter has been producing wonderful collectable specimens for several decades; these include octahedral acanthites, dyscrasites, various silver-mercury amalgams, some of the world’s best xanthoconite, and is the type locality for imiterite. Proustite is well known from the mine, but most of the crystals have been small. The specimen below is a large cauliflower like clump of crystals (the specimen weighs just under 3 pounds!) with individual crystals that are up to a cm across and several cm tall. It is impossible to know for sure when this specimen was recovered – it is clear that it was smuggled out of the mine, and passed through local merchants before coming to the US in late 2014.

13 cm cluster of proustite crystals from Imiter, Morocco (Jeff Scovil photograph). This small cabinet sized specimen is solid proustite, and contains individual crystals to 1.8 cm on a side. The luster, and deep vermillion color, and overall size make this a modern “classic”.

Although this is hardly a “classic” proustite as compared to a sharp dog’s tooth from Charnarcillo or individual cherry red crystal from Schneeberg, it is an amazing specimen. The Imiter Mine had a capacity of 300,000 metric tons per year (t/yr) of ore and surely will continue to produce interesting specimens.

Metal mines of the Anti Atlas mountains in Morocco. Imiter is one of the largest silver mines in the world, and is a large open pit.

When will the Golden Age Wane?

Malthusian theory would predict that demand will outstrip supply in the future – maybe the near future. But mineral collecting is not dead, and in fact there is as much evidence based on the last 30 years that there will even more high quality specimens exchanging hands for decades to come. Why is Malthusian theory is wrong? Because demand for minerals – both as a commodity and as a collectable – is higher than it has ever been, and the world is responding. More mines, more mining, and more money in minerals.

Global silver production – looks just like the global growth in population! Each and every mine has the potential for specimens and even though historic localities are exhausted, new horizons are bright.

It is certain that the market of “art” will be what mineral collectors will have to deal with in the next quarter century. If history of the art markets are predictors for minerals, there will be periods of malaise; but even during these periods the assessed worth of classics had an average annual escalation of several percent. This leads to another question – where the heck do all these wealthy people come from? Again, there are detailed studies of the art market, and one of the alarming (alarming if you are a collector, perhaps enticing if you are a dealer) lessons learned is that globalization will dramatically increase competition at the highest end. However will mineral collecting evolve with a very stratified market? That experiment is being played out in real time, and I hope for “niche markets” to develop – but that has not happened yet. Hold on to your wallets, the golden age squeezes…….

The World’s Greatest Mineral Rush: Uranium Minerals of the Colorado Plateau

My experiments proved that the radiation of uranium compounds … is an atomic property of the element of uranium. Its intensity is proportional to the quantity of uranium contained in the compound, and depends neither on conditions of chemical combination, nor on external circumstances, such as light or temperature — Marie Skłodowska Curie, Polish/French scientist who won 2 Nobel Prizes; her doctorate thesis was the first to show that radiation came from an atom, not from environmental conditions.

When rock blooms yellow and Geiger counters rattle – uranium! From a National Geographic Society publication, 1953. Click on any figure for a larger version.

The theme of the 2015 Denver Gem and Mineral show is “Minerals of the American Southwest”. The theme evokes images of colorful copper minerals from Arizona, gold and silver from Colorado, red beryl and champagne topaz from Utah, and perfect fluorites from Bingham, New Mexico. The four states have a rich mining heritage with boom towns, barons, and villains. The influence of the American Southwest on the modern mineral collecting hobby is also outsized – from personalities of famous collectors and mineral dealers to mega mineral shows, perhaps no geographic region is more influential. The southwest was also the site of the greatest mineral rush in history, but is largely unremembered – the great uranium rush of the 1950s.

My father and I visited many of the uranium mines – mostly the abandoned ones in Utah – in the early 1970s, and I collected a boat load of “yellow smears”. I learned how to read the x-ray diffraction films from studying samples I prepared for identification. I was cautioned to store these treasures in the barn rather than my bedroom because of issues with radon or radioactive decay. I never really built a systematic collection, and my specimens were eventually disposed of for environmental reasons, but I was fascinated by the story of the uranium minerals. In 1974, I read Edward Abbey’s book Desert Solitaire, and was deeply affectedly by his descriptions of the joy of isolation and the beauty of the canyon country and mountains around Moab. I also saw in this book the tremendous loss that we experience when we destroy wilderness. I was asked to talk at the 2015 Denver show on minerals of the southwest, and it was assumed I would wax on and on about the silver minerals…but I decided to revisit uranium!

Small crystal clusters of carnotite, largest cluster is 0.7 mm across. San Juan Co., Utah

The launch of the Manhattan Project in 1939 suddenly made uranium a valuable commodity, but established mines were few globally; in the US only a few mines in western Colorado were producing any uranium (mainly as a byproduct of vanadium mining). Leslie Grooves, director of the Manhattan Project secretly purchased the entire stockpile of Vanadium Corporation of America, which was stored at Uravan, Colorado – but that was only 800 tons of ore. Once the war was over the US had less than 100 pounds of enriched uranium (U235), and development of domestic uranium mining became a government priority. The newly minted Atomic Energy Commission announced remarkable incentives for new uranium discoveries: a price of $3.50 per pound of uranium oxide, and a $10,000 bonus paid on the delivery of 20 tones of ore that assayed 20 percent uranium oxide. By the early 1950s there were more prospectors looking for uranium on the Colorado Plateau than ever mined gold in the history of California – in fact, there were 30 uranium “rushers” for every 1 ’49 rusher to the Sierra Nevada.

Hundred’s of articles appeared in the early 1950s publicized the “rush” for uranium. Many of these articles were funded by the AEC and suppliers of geiger counters.

The AEC incentives worked — by the mid-1950s there were about 800 major uranium ore producers on the Colorado Plateau, and ore production was doubling every 18 months. The rush made more millionaires than the great Colorado silver rushes of the 1870s or the Arizona copper rushes of the 1880s. Moab, Utah was dubbed the “Uranium capital of the World”, and had 20 millionaires for every 250 citizens. The AEC cancelled the bonus for uranium production in the early 1970s, and eventually the mining industry declined to a subsistence level. However, the rush to the Colorado Plateau had a huge impact – from 1949 to 1971 the mines produced about 400 million tons of ore that yielded 200,000 tons metric tons of uranium metal.

Coincident with the great uranium rush, mineral hobbyist clubs and minerals shows exploded – the American Federation of Mineralogical Societies (AFMS) was founded in 1947. Although it is a stretch to directly connect the great uranium rush with the rise of mineral collecting as a hobby, it is obvious that the heavy promotion of uranium prospecting peaked the interest of many Americans, and rock hounding entered a golden age. Many collectors purchased or collected uranium minerals from the Plateau, and these prizes sat in places of honor in the collector’s cabinets. However, as the hazards of uranium mining became understood in the 1970s, collectors began to dispose many of their specimens. Today, it is almost impossible to find a fine Colorado Plateau uranium mineral specimen – and the heritage of an amazing American event has faded from the public memory.

Map showing the location of uranium mines in the US. The data is from a EPA data base, and does not show the size of the mine. However, the density of the mines is a good indication of the richness of the deposits.

A Brief History of the Colorado Plateau Uranium

The history of uranium on the Colorado Plateau begins a half century before the Great Rush when prospectors were looking for the more valuable commodities of radium and vanadium. Settlers in the Paradox Basin in southwest Colorado knew of a yellow, powdery material found in sandstones before 1880; it is likely that Ute and Navajo Indians collected this same material as a pigment for hundreds of years. By the late 1890s various prospectors had collected a few hundred pounds of the material, but did not know what it was, nor could they find a market. In 1881 Tom Talbert discovered the same yellow material in Montrose County, and eventually this material found its way to Gordon Kimball in Ouray. Kimball sent samples to Frenchman Charles Poulot (residing in Denver) in 1898, who determined it contained both uranium and vanadium. Poulot gave the material to M. M. C. Friedel and E. Cumenge (of Cumengite fame) who determined an approximate formula: K2(UO2)2(VO4)2·1-3H2O Also in the samples were significant amounts of radium – which is a decay product of U238. This coincided with Curie’s discovery of the element radium, and she began to purchase carnotite from Colorado for research. Radium became the vanguard material for worldwide research on radioactivity, and a number of mines were staked along the Colorado Plateau.

Colorado radium played a very significant roll in the lab of Madame Curie, and was essential to define the unit of radioactivity, the Curie.

Aside from staking claims, nothing of substance happened in carnotite mining until 1910 when a new medical market for radium developed — it appeared to have a dramatic effect on certain cancerous tumors — and southwestern Colorado became a major supplier. However, the outbreak of WWI completely quashed the demand. As the demand for radium dried up, the demand for vanadium increased rapidly. It was discovered early in the 20^th century that adding a small amount of vanadium increased the strength of steel. In 1905 Henry Ford was introduced to a vanadium rich steel, and was so impressed with its characteristics, he used it in the chassis of his Model-T. By the end of WWI the carnotite mining shifted from the focus on recovering radium to vanadium, and by 1922 radium recovery ceased all together. Although the demand for vanadium was cyclic, by about 1935 it had become an important enough metal that Vanadium Corporation of America purchased most of the former carnotite mines, and founded the town of Uravan (contraction of uranium and vanadium).

Location of the carnotite deposits mined for radium and then vanadium before WWII. From Chenoweth, 1981.

After 1936 there was a steady increase in prospecting and development of properties along the Utah-Colorado border targeted the Morrison Formation (Jurassic age), in particular, a fluvial sandstone/mudstone unit called the Salt Wash Member. With the outbreak of WWII steel became essential; vanadium was declared a strategic metal, and more than 600,000 tons of vanadium ore with a 2% grade was produced.

Mine and mills at Uravan, ca 1935

The modern era of uranium exploration and mining on the Colorado Plateau began when the Atomic Energy Commission was established by the Atomic Energy Act of 1946. All functions of the Manhattan Project, including the acquisition of uranium, were transferred to the ACE at mid-night, December 31, 1946. The AEC set up a procurement shop in Grand Junction, Colorado and begin devising schemes for securing uranium. At the time there were only 15 mines operating on the Colorado Plateau, and uranium was still considered a lesser product than vanadium. The AEC was the only buyer of uranium, and thus, set a price they thought would incentivize production; it soon became apparent that the AEC also had to be involved in the milling of ore, and provided bonuses for uranium oxide concentrations. The very first procurement contract was signed with Vanadium Corporation of American on May 28, 1947. The AEC demanded a rapid expansion of exploration and mining efforts, and provided assistance by undertaking geologic surveys and providing free assay services.

Between 1948 and 1956 the AEC and the USGS tasked several hundred geologists to scourer the Colorado Plateau and make their maps and drilling core results freely available to prospectors. The AEC also built more than a thousand miles of roads across the plateau to promote access to the most remote regions. Prospectors and weekend treasure hunters flocked to Utah and Colorado, and later to New Mexico and Arizona. Some of these prospectors struck it rich, and lived life higher than the biggest copper or silver baron of the 19th century. One of these “lucky” prospectors was Charlie Steen.

For two years Steen roamed the area around Moab, Utah and “barely” subsisted with his family in a trailer and tar paper shack. Using his experience in the oil industry, he was certain the uranium would collect in anticlines – sort of like an oil trap – and he drilled haphazardly. On July 6, 1952, Steen drilled into an incredibly rich deposit of “pitchblende” (uraninite) at 200 feet depth, and over the next year developed the Mi Vida mine. The fact that the ore was uraninite – not carnotite- in a rock type previously not shown to carry uranium, and at a depth that similarly unexpected, caught the government geologists by surprise. Steen became a multi-millionaire, and his find electrified the country – and greatly accelerated the rush to the plateau!

Charlie Steen underground with his son at the Mi Vida Mine, ca 1955

Geologists began to understand the nature of the Colorado Plateau uranium deposits in the late 1950s. Garrels and Larsen (1959) published USGS professional paer 320, Geochemistry and Mineralogy of the Colorado Plateau Uranium Ores, and it became clear that hydrology was the most important factor in localizing the uranium in vast columns of sedimentary rock.

Uranium deposits on the Colorado Plateau in 1959 with a size of more than 1000 tons.

Uranium is found in more than a dozen sedimentary strata on the plateau but the Morrison formation of late Jurassic age and Chinle of Triassic age account for 95% of the produced uranium. The Morrison was formed from the erosional sediments derived from a highlands called the Elko that existed along what today is the Utah-Nevada border. These sediments were deposited in floodplains, river channels and swamps, not unlike the Mississippi delta today. The Chinle is dominated by eolian (wind-driven dunes) deposits with smaller river channels cut during intervals of more precipitation. The uranium appears to have mobilized by ground water; dissolving and moving sparsely concentrated uranium and precipitating and concentrating that uranium when structural or chemical boundaries are encountered. The deposition of the uranium occurred millions of years after the deposit of the sedimentary rocks — perhaps 100 million years later. The deposition is most signifiant where the sediments contained trapped organic materials – logs in river channels or organic ooze in swamps. In fact, there are many examples of petrified logs that have been completely replaced by uraninite or coffinite.

The real key to the Colorado Plateau deposits is the long term stability of the sediment column. This stability has allowed dilute solutions to build these diffuse deposits. This is not the best environment to grow beautiful crystals, but small variations in chemistry has allowed for a wide range of uranium minerals. Through 2010 the Colorado Plateau has produced more than 600,000 tons of uranium oxide – and today contains 15% of the worldwide uranium reserve.

High purity uranium “biscuit”. Uranium metal is not known in nature.

Colorado Plateau Uranium Minerals

The mineralogy of uranium is a fascinating and complex topic – the nearly ubiquitous presence off U in the environment, its large atomic radius, strong affinity for oxygen (lithophile), and high solubility in certain valence states leads to large number of secondary uranium minerals. The lithophile nature of U also means that 4.5 billion years of Earth evolution has concentrated the element in the crust; the statistic abundance of U in the crust is 2.7 ppm, as compared to 0.075 pm for silver and .004 ppm for gold. In other words, there are 675 atoms of uranium for every atom of gold in crustal rocks!

Relative abundance of elements from cosmology, normalized to the abundance of Si. Note that uranium, as expected with its large Z, is much rarer than lighter elements. It is a few orders of magnitude less common than gold. However, uranium is strongly lithophilic, and has been concentrated in the Earth’s crust to the point that it is more common on the surface than either gold or silver.

The fact that uranium has been so strongly enriched in the crust is also one of the reasons it is so ubiquitous – traces can be found in every rock type, soils and water. Uranium is a “5f electron” element, which controls much of the way it behaves in the environment. 5f refers to the electron configuration, or the distribution of electrons about the atom; uranium is an electron donor and has four different valence states depending on environmental conditions. Two of these states, U4+ and U6+, are stable in geologic environments. In igneous environments the +4 valence state prevails, and uranium is one of the last elements to form minerals in a magmatic or hydrothermal fluid. By far, the most common mineral to form in igneous environments is uraninite (UO2). However, once that uraninite is exposed to a humid and oxidizing environment the surface of the uraninite undergoes oxidation and the U4+ → U6+; the higher valence state is incompatible with the uraninite structure, and the uraninite decomposes, releasing the U6+, which rapidly binds with two oxygen atoms to form the uranyl ion [UO₂]²⁺

The uranyl ion has a linear structure, with very strong bonding between the uranium and oxygen, and it is highly soluble in ground water. This high solubility leads to extraordinary mobility of uranium, and a key contributor to Colorado Plateau deposits. The uranium mined today in Grants or Paradox Basin did not originate anywhere near those locations; it likely was deposited in minor uraninite deposits during the billions of years of mountain building in what has become the North American Plate. Decomposed, oxidize, and transported through great distances, the uranium was concentrated when subtle encounters with ground water chemistry changes.

Paragenetic sequence of uranium minerals — from primary uraninite with a +4 valence to hundreds of uranium minerals with a +6 valence (from Plasil, 2014).

The mineralogy of U6+ is very diverse because of the uranyl ion; it has a linear, dumbbell shaped structure that cannot be easily substituted by other high valence cations. The uranyl ion will most commonly attach to tetrahedral anion groups; SO4, PO4, AsO4, SiO4. Any charge balance is then accommodated by other cations. The figure above is a generalization of the paragenes of uranium minerals; at the top is the primary oxides and moving down the chart shows the minerals that form as uranyl migrates away from the primary source. Typically uranyl carbonates form first, and vanadates – like carnotite – form far from the original source and after many generations of mineral growth and decomposition.

There are about 160 different uranium minerals known, and 61 have been reported as coming from the Colorado Plateau, and 12 have the Plateau as their type locality (there are dozen uranium minerals yet to be characterized for the Plateau deposits). The names are mostly unfamiliar to collectors – things like Becquerelite Ca(UO2)6O4(OH)6 · 8H2O, Schrockingerite, NaCa3(UO2)(CO3)3(SO4)F · 10H2O and Rabbittite, Ca3Mg3(UO2)2(CO3)6(OH)4 · 18H2O. They have colors that span the rainbow, although bright yellows and deep greens are favored. Those minerals that contain the uranyl ion all fluoresce (although U4+ minerals do not), and differences in hydration – and loss of water with alteration – changes the fluorescence. Unfortunately, the sedimentary deposits of the Plateau do not lend themselves to environments in which large, distinct crystals grow. Below is a gallery of some of the more important uranium speciemens:

Carnotite K2(UO2)2(VO4)2 · 3H2O

Carnotite, Happy Jack MIne, Utah. BYU collection.

Carnotite crystals, to 2 mm. Monument Valley, Arizona. Stephan Wolfsried photograph and specimen.

Coffinite U(SiO4)1-x(OH)4

Coffinite, Mount Taylor deposit, Ambrosia Lake area, Grants District, McKinley Co., New Mexico. Field of view is 3cm.

Uraninite UO2

Uraninite, Big Indian District, San Juan Co., Utah.

Tyuyamunite Ca(UO2)2(VO4)2 · 5-8H2O

Tyuyamunite, Paradox Valley, Montrose Co., Colorado. Dave Bunk collection, Jesse La Plante photograph.

Zippeite K3(UO2)4(SO4)2O3(OH) · 3H2O

Zippeite, Big Gypsum Valley, San Miguel Co., Colorado. Dave Bunk collection, Jesse La Plante photograph.

Unknown Uranium Carbonate

Slick Rock, San Miguel Co., Colorado. Dave Bunk collection, Jesse La Plante photograph.

The uranium minerals were intimately associated with vanadium minerals – often these carried some amount of the uranyl complex. The Colorado Plateau vanadium minerals are as unique as their uranium counterparts, and often even more colorful and unusual. A few are featured below:

Schrockingerite NaCa3(UO2)(CO3)3(SO4)F · 10H2O

Schrockingerite, Monogram Mesa, Montrose Co., Colorado. Dave Bunk collection, Jesse La Plante photograph.

Metamunirite NaVO3

Metamunirite, Burro Mine, Slick Rock, San Miguel Co., Colorado. Dave Bunk collection, Jesse La Plante photograph.

Metahewettite CaV6O16 · 3H2O

Metahewettite, Hummer Mine, Uravan, Montrose Co., Colorado. Dave Bunk collection, Jesse La Plante photograph.

Pascoite Ca3(V10O28) · 17H2O

Pascoite, Big Gypsum Valley, San Miguel Co., Colorado. Dave Bunk collection, Jesse La Plante photograph.

Metarossite Ca(V2O6) · 2H2O

Metarossite, Arrowhead Claim, San Miguel Co., Colorado. Dave Bunk collection, Jesse La Plante photograph.

Hewettite CaV6O16 · 9H2O

Hewettite, Hummer Mine, Uravan, Montrose Co., Colorado. Dave Bunk collection, Jesse La Plate photograph.

Paradise Lost

The Great Uranium rush was over by the early 1960s. Many lone prospectors roamed some of the most desolate and beautiful country in the world in search of radioactive treasure. Uranium mining in the 1960s was controlled by large corporations, and huge open pit mines like Jackpile east of Grants, New Mexico supplied tons of uranium. By 1971 the government had more uranium than it could possibly use, and cancelled the incentives. By 1980 the world market drove the prices for the silver-colored metal to prices that shut down even the largest producers. Today the prices occasionally spike, leading to much discussion about reviving mining on the Colorado Plateau. However, the heavy environmental toll has a very dark legacy. It is unlikely that there will ever be another uranium mine in the Triassic and Jurassic sandstones that make the plateau look like the landscape of Mars.

101 spinel twins: symmetry and beauty in silver

The universe is built on a plan the profound symmetry of which is somehow present in the inner structure of our intellect, Paul Valery, 19th century French Poet

Silver, Kearsarge Mine, Houghton Co., Michigan. The specimen is 3.5 cm across. This native silver is a lustrous example of a “weave” of sliver crystals exhibiting spinel twinning. Photograph by Jeff Scovil. Click on any photo in the article to get a larger view.

When I first started building a mineral collection — back about 1960 — the single most compelling criteria for determining if a specimen was a “keeper” or just something for the beer flats filled with colorful, yet, unworthy rocks, was whether there was a euhedral crystal. My fascination with the perfection of a sharp crystal face is not at all uncommon for beginning collectors. The fact that nature could take time to construct something so perfect strikes a deep chord; the vast universe created by the ultimate act of violence – the big bang – and ruled by entropy, and inevitable decay, still values symmetry. I recall an early discussion with my mother on the beauty of spring flowers – I asked her why she thought they were beautiful, and she responded with a joyful exposition on the bright and varied colors and the delicate nature of the pistil, and remarkable symmetry of the petals. I told her that the petals were exactly like crystals since they are always alike, and must be following some sort of “rules”.

The English word symmetry comes from the Greek symmetria; in turn, symmetria is a concatenation of Greek words sun and metron, meaning “together” and “measure”. There is a substantial body of Greek literature that refers to symmetry as “harmonious and beautiful proportion and balance”. This philosophical definition of symmetry deviates from the strictly mathematical definition, but still projects the power of something that is predictable and has a geometric balance to be pleasing to the eye. This “pleasing to the eye” is a euphemism for beauty — hard to define exactly, but beauty excites our aesthetic senses.

To me, there is nothing more pleasing to the eye than a silver specimen exhibiting spinel twinning – repeating patterns of crystals that produces a highly geometric weave. The photograph at the top of the column is a silver from the Kearsarge Mine, Houghton Co., in the Upper Peninsula of Michigan. The specimen is defined by a central rib — an elongated stack of silver octahedrons, and branches intersecting the this rib at angles of approximately 60 degrees. In turn, these branches have secondary branches exiting at similar angles. The repeating geometry yields a specimen architecture that is clean and sharp – an exemplar of what the Greeks meant by symmetry.

Silver, from a locality near Tongchong, Yunnan Province, China. Specimen height is 6cm. The wires are the result of decomposition of acanthite. Jeff Scovil photograph.

Silver: a special element

Silver is a remarkable element that can form an array of minerals; about 180 different species. Thankfully, elemental silver is sufficiently inert to occur in nature and is widely distributed throughout the world. Native silver is a metal of bright white color; it has the highest reflectivity of any metal. Silver is also the best metallic conductor of heat and electricity and extremely malleable and ductile. These properties are, of course, a result of crystal and atomic structure, which is a face-centered cube with metallic bonds. The atomic radius of silver is nearly identical to that of gold – and gold commonly substitutes into the silver crystal lattice.

Native silver crystal forms, from Goldschmidt (1913). The octahedron is most common, although cubes are much coveted by collectors. The bottom 3 figures show spinel twinning.

Silver crystallizes in the isometric system, and although individual, sharp macro crystals are rare, the octahedron and cube forms are most common. The largest individual crystals are from Kongsberg, Norway, where some octahedrons 3-5 cm on a side grace a few fortunate collections.

Cubic silver in calcite; Kongsberg, Norway.Each of the large cubes are approximately 1 cm on a side. Jeff Scovil photograph.

As a rule, crystals of silver are equi-dimensional or platy. The platy nature comes from the propensity from silver to twin (this is similarly seen in gold and copper) on octahedral faces {111}. This twinning is known as spinel twinning and is described below. The conditions for when spinel twinning occurs appears limited – although silver masses of spinel twins are known from hundreds of locations, there are only three or four localities where this type of silver crystallization is common. The two most famous localities are Batopilas, Mexico and Chanarcillo, Chile.

By far, the most common form of silver in a mineral collections is the wire – which is a secondary growth from the decomposition of silver sulfides and sulfosalts. Any silver deposit that undergoes supergene enrichment inevitably has silver wire specimens. The picture at the top of this section of the article is a fine silver wire mass from Tongchong in China. The wires in this specimen are attached to a very small piece of acanthite, no doubt the host material that provided the silver. All silver sulfides and most silver sulfosalts will produce silver wire upon disassociation — especially promoted by heating. Although wires can be extremely interesting and coveted specimens for collectors, there are been numerous cases where the wires were “grown” by unscrupulous collector/dealers and passed off as “natural” specimens.

Beauty in Nature

When I hear the word “beautiful” used to describe minerals by collectors I often ask what they mean. More often than not, the answers seem wanting to me. Mostly, it is about color — pink and red minerals are always “beautiful”, but black and brown minerals are “interesting”. Although color can transfix, and certainly evoke emotion, I can not relate to it as the primary metric of natural beauty. I am also looking for structure in my surroundings – a window into the soul of nature, order out of the chaos all around me.

A seminal event for me was attending “math summer camp” during the summer between 7th and 8th grade. The instructor was an outstanding teacher named Jack Gehre, and his focus was geometry and trigonometry. Early in the class Mr. Gehre introduced Euler’s formula; for any normal polyhedron, the sum of the number of faces plus the number of vertices, minus the number of edges always equals 2. I spent the rest of the summer camp trying to understand why. I suddenly had a “rule” in nature that I could apply to my mineral collection — a rule mysterious and powerful, but incredibly simple. It was beautiful. I did not know much about Euler then, but later in college I was introduced to another “law” by Leonhard Euler — an incredible 18th century Swiss mathematician — that has to be the most beautiful equation in all of nature. I was in a class on series analysis, and the professor, Alan Sharples, walked in the first day of the semester and wrote the following on the black board:

Sharples said, “this is Euler’s identity, a remarkable assertion. Prove it. That is all for this first day of class.” Turns out that this is pretty easy to prove, but when I viewed this on the blackboard I was transfixed — it was pure beauty. Imagine three essential mathematical constants – e, pi, and i – combined to equal -1. Wow – simple, brief, and exact. To this day I view this as a definition of beauty (Euler’s identity is routinely identified as the one of the most beautiful equations in science).

Euler’s identify may seem a long ways from realm of beauty in the mineral kingdom. However, to me, they are very much related. Simple, surprising, and an expression of natural symmetry.

Herringbone silver mass, Batopilas, Chihuahua, Mexico. The Specimen is 3.75 cm across. Jeff Scovil, photograph.

Respect the Spinel Twin

Crystal growth in nature is quite complex; the crystal form, crystal size, crystal chemistry all are expressions of the paragenesis. Crystallization for most geologic materials involves the precipitation of a solid (the crystal) out of a solution or solvent (usually hot thermal fluids, although solutions of nearly any temperature can carry dissolved loads of ions and cations). Crystals start with nucleation of a few molecules from the solution, and then growth occurs by pulling the necessary ionic components out of solution. The rate at which individual crystals grows depends strongly on the saturation level of the ions of interest – supersaturated solutions appear to be able to grow crystals at extraordinary rates (at least compared to geologic time!), sometimes at several cubic cm per hour.

It is not clear who first recognized twinning in crystals, but it was first written about in detail by Rene-Just Haüy in his epic tome Traité de Minéralogie, published in 1801. In the beginning part of the 20^th century there were a number of studies to understanding twinning in minerals. The classic definition was introduced by Friedel in 1926: A twin is a complex crystalline edifice built up of two or more homogeneous portions of the same crystal species in contact (juxtaposition) and orientated with respect to each other according to well-defined laws. The “well-defined laws” all are based on some simple ideas, the most important of which is that within a crystal core that a least one lattice row (i.e., a crystal edge) is common to two different crystals. The figures below illustrate this concept — the lattice of a cubic crystal is defined by four points, and a plane can be drawn through these points that allows a second crystal to share lattice points but have a rotated orientation. Twinning adds symmetry to a crystal aggregate, most commonly about a rotation axis or reflection across a plane. In the metals copper, gold and silver, a particular type of twin is common, called the spinel twin.

Spinel twins are so-named because it is a very common habit seen in the mineral spinel. They are contact twins, meaning that have a planar composition surface shared by two individual crystals; this surface is along an octahedral face (written as {111}), and means that there is a rotation of 180^o about the contact plane. This is illustrated by the lower figure above – there are two octahedrons joined along a contact plane, but the top terminations “point” in directions and are separated by 120^o. The figure below shows how spinel twins can be flattened, and give the characteristic triangular faces that are seen on platy crystals of silver (and gold).

Notional relationship between an octahedron and a spinel twin producing a triangular type crystal face. This is “notional” in that this is NOT how the spinel twin evolves with time, but rather, a visual guide to compare an octahedron (left) and triangular face (right).

In silver, spinel twinning almost always repeats itself with regularity, producing a pattern that resembles a weave of wires. The silver at the top of this section of the article is from Batopilas, Chihuahua, Mexico, and is an example of a mass of spinel twins. Through the middle of the specimen is a series of parallel elongated crystals, and growing “off” these strands are regular strands oriented at 60 degrees (or 120 degrees, strictly speaking). These are all spinel twins – repeating some natural frequency that is due to a long lost geologic condition. Once assembled, the spinel twins from an aggregate of crystals that has been called a “herringbone” silver in reference to the similarity to the shape of the rib cage of the smelly game fish beloved by the peoples of the Baltic.

Why do spinel twins form in silver? Under certain ideal conditions, a single large crystal represents a “minimum” energy condition, and thus is due to an important thermodynamic rule — a chemical system will stabilize at state of least energy. If individual crystals are a minimum energy state, then twinned crystals are by necessity at state of higher energy, and thus should be rare. However, environmental conditions tend to localize energy states; for a supersaturated solution, the crystal growth is extremely rapid, and twinned crystal allow more ions to join a crystallize aggregate faster, thus minimizing a local energy state. For all “herringbone” silver specimens it appears that the conditions of formation require a supersaturated solution, low in concentrations of sulfur, and extremely rapid crystal growth. These conditions are relatively rare in most epithermal vein deposits; it is very uncommon to find a spinel twinned silver specimen from the great silver deposits of Colorado, Ontario or Freiberg!

Large silver plate (7.5 cm from side-to-side) from Chanarcillo, Chile. The specimen is a weave of spinel twins – and is my favorite silver specimen in my collection. Jeff Scovil photograph.

The silver pictured above is my favorite native silver in my entire mineral collection. This is a large “herringbone” plate with a three dimensional repeating pattern of twins. The specimen represents something remarkable in turns of crystal growth. The tiniest variations in chemistry or temperature during growth would have truncated the growth of this silver weave.

Close up of the Chanarcillo specimen shown above. The central rib is an elongated chain of octahedrons. Field of view is 3 cm. Repeatedly, silver crystal “twin” off the octahedral face(s). At the very top of the specimen there are identifiable octahedrons.

A close examination of the Chanarcillo herringbone yields views of spectacular detail – endlessly repeating, and shouting the fundamental rules for symmetry in crystals. Along the edges of the crystalline mass you can see individual octahedrons – the termination of various elongated crystals.

Beauty and the pretenders

Rapid growth in silver often produces crystalline masses that are complex. However, spinel twins are distinct, and uncommon. Rapid growth often leads to dendritic masses – mostly silver feather patterns or strings of stacked cubes. These dendrites are not spinel twins; in fact, instead of fundamental order, they represent chaotic growth. Although there is some sense of beauty in the randomness of dendrites, it is mostly through “self-similarity” – various patterns that appear to scale with size. This is fundamentally different than ordered spinel twins – and in many ways points to disordered processes. I am always shocked (okay, probably an overly harsh expression of emotion) when I find dealers selling “herringbone” silvers that are in fact dendrites. That is like marketing hamburger as Filet Mignon. Similarly, silver wires can certainly be attractive; however, they are products of mineral destruction not construction. To me, beauty in silver spinel twins is about construction, order, and symmetry. Defining beauty will allows be in the eye of the beholder — it is just better when there are rules involved.

The Glue Does Not Show: Mineral restoration and specimen value

Shades of grey wherever I go
The more I find out the less that I know
Black and white is how it should be
But shades of grey are the colors I see

Billy Joel, Shades of Grey, released 1993.

Stephanite, Husky Mine, Mayo Mining District, Yukon Territory, Canada. The crystal group is approximately 6.3 cm across, and outstanding for the locality; Husky Mine polybasite and stephanites typically have an iridescence that it probably caused by light reflection/refraction in a very thin coating of an unknown silicate. Jeff Scovil Photo.

In the mid 1980s I was first asked to be a judge of the competitive mineral exhibits at the Tucson Gem and Mineral Show. At that time the TGMS competition, and its two top awards – the McDole Trophy (best case of minerals entered into competition) and the Lidstrom Trophy (best individual mineral entered into competition) – were considered the pinnacle of the mineral world. The winners of these awards looked like a “Who’s Who” of the mineral collecting community, and every year the competition was passionate and savage. The rules for the McDole and Lidstrom awards were few; it was based on the judges experiences, biases, and an element of luck on who decided to enter the competition. The judging for the McDole and Lidstrom awards was also a “discussion” rather than some type of formal poll — a judge with a domineering personality could filibuster the other judges into accepting his or her opinion. I recall clearly the discussion around a particular specimen entered into the Lidstrom competition that I was fond of; “We can’t possibly consider that specimen a best – it has been repaired!” The pronouncement carried such an air of academic certitude that I immediately agreed. Of course, it had been repaired! How could it really be a great mineral specimen if there was some glue involved!

It was not too long after that I began to ponder the absurdity of dismissing anything that is repaired as inherently flawed (on a personal note, now that I have multiple metal parts in various joints, I embrace the repaired). Repairing a mineral is rather common – mineral extraction is inherently a violent activity, and the very act of handling a specimen introduces the possibility of drops, dings and scratches. But there is still a feeling that repairs should affect the monetary value of a specimen. I don’t think I have ever been to mineral show where I have not heard some version of the conversation between a dealer and a collector where the potential purchaser doesn’t ask for a significant discount because the specimen has been repaired. The stephanite pictured at the top of this article is a fantastic complex crystal from the Husky Mine in the Yukon Territory, Canada. I first committed to buying this piece for my collection around the year 2000. However, when I went to go pick it up from the dealer I opened the box and the marvelous sample of “brittle silver” was in three pieces! The stress of transport had caused the crystal to part along inter-growth boundaries. I was heart broken, and walked away from a masterpiece. The dealer repaired the piece expertly, and eventually I was able to acquire it. However, several years later I was transporting it to be photographed and it “parted” again! Fortunately, it was once again restored, and now sits permanently in my mineral cabinet never to travel again. I believe it is the best, or one of the best, Husky Mine stephanites in existence, and the fact that it has some clear cyanoacrylate helping to hold it together is inconsequential.

Repair would, thus, seem to be a rather “black and white” issue – restoring a collectable to its original configuration is not fraud or even misrepresentation of nature. Sadly, it is not “black and white”, and repair/restoration has become a spectrum disorder in the mineral collecting world. Today many consider filling missing gaps in crystals with acrylic resin, buffing away scratches on crystal faces or even heating a specimen to “restore” its primordial color as simply “sophisticated repair”. Not black and white, but shades of grey.

The Pieta, carved by Michelangelo in the 16th century. The statue has been repaired a number of times in the last 500 years — most recently removing the damage done by a geology hammer (!) wielded by a lunatic.

Real Repairs

The Pieta is a signature masterwork of Italian sculptor Michelangelo, and one of the most famous works of art in history. Michelangelo was only 23 years old when he carved the single block of Carrara marble into a haunting image of a crucified Jesus being held by his mother. By any figure of merit, the Pieta is priceless. Yet, it is repaired – several times! The four fingers of Mary’s left hand were snapped off during a move in the 18^th century (restored in 1736). The most egregious damage occurred in an instant of insanity when Laszio Toth, an unemployed Hungarian geologist attacked. Toth struck the Pieta more than a dozen times with his field hammer, breaking off Mary’s arm, part of her nose, and chipping her face.

Mary’s hand after the Toth attack. More than a hundred fragments of marble had to be reassembled to restore the Pieta.

The repair of the statue was done by a team of 10 people painstakingly reassembling the fragments and filling in voids with a mixture of powdered marble and polyester resin. When the restore work was unveiled it was claimed that it was impossible to identify where the damage had been. Some experts suggest that with the passage of time the resin has perceptibly changed color, but in general the repair has faded into history and the magnificence of the Pieta has been restored.

The restoration of the Pieta might be a fanciful stretch as an analogy for mineral repair, but it does frame the philosophy of specimen “value”. It is highly unlikely that the reconstruction of Mary’s left hand would effect the value of the Pieta if the Vatican decided to part with the treasure; I can’t imagine any art collector asking the Vatican for a “discount” because the marble was not exactly as Michelangelo carved it long ago. On the other hand, the restoration process went to great lengths to assure that nothing changed from the original – no added expression to Mary’s face, no extra lamb seated at her feet.

The Alma Queen; a 10 cm, complex rhomb of rhodochrosite perched in a matrix of fine quartz crystals. This “rock” was found in 1966 at the Sweet Home MIne, and has been called the finest mineral specimen in the world.

The Rhodochrosite Royalty – a family full of plastic surgery

In 1966, a 90 year old silver mine located on the slopes of Mt Bross – one of Colorado’s 53 peaks that have elevations in excess of 14,000 feet above sea level – yielded a remarkable mineral specimen. The mine was called the Sweet Home, and during its on-again, off-again mining history had periodically produced some of the world’s best rhodochrosite. However, the standard for rhodochrosite was reset when a mining crew drilled into a pocket and found a 10 cm rhombohedron of cherry red rhodochrosite perched on a slab of pencil thin white quartz. The specimen was purchased by one of Colorado’s earliest fine mineral dealerships, Crystal Gallery, for the princely sum of $2500. Crystal Gallery was a partnership between Merle Reid and Colorado collector legend George Robertson. The rhodochrosite ended up in the hands of Peter Bancroft (much to the chagrin of George Robertson), who christen the piece as the “Alma Queen”, in recognition of the mining town a few miles southeast of the Sweet Home Mine (the picture above is “official” photo of the Alma Queen from its present home, the Houston Museum of Natural Science). In short order the Queen passed through a hands of a number of famous mineral dealers, finally becoming a prized possession of Perkins Sams. In 1986, Sams sold the Queen to Houston Museum – and a few years later it was being moved and was broken! Actually, it was not too surprising given that the rhodochrosite has perfect cleavage, and the huge crystal was isolated and perched on matrix. Fortunately, the crystal was “repaired” – it is impossible to see the glue reattaching the rhomb – and is still considered a masterpiece.

The Alma Queen enticed others to want to return to the Sweet Home Mine and search for more rhodochrosite. In 1991 Bryan Lees and partners began a professional and systematic exploration for mineral specimens. In 1992 Lees’ operation discovered a 1.5 meter long pocket that yielded incredible — larger than even the Alma Queen — specimens. Most of the crystals were detached from matrix, jarred from their natural perches by the mining activity. The largest of the crystals was more than 15 cm across, and was dubbed the Alma King.

Bryan Lees holding the Alma King, just outside the Rainbow Pocket. The crystal was some 15 cm across!

The Alma King was eventually reattached to matrix, and was brought to the Tucson Gem and Mineral Show in 1993. I remember seeing the specimen, and was stunned. I also recall standing next to a old time collector who remarked “too bad it is repaired”. Wow – my thoughts were not conflicted at all – the repair was sincere and returned a natural masterpiece to it’s rightful magnificence. It was exactly like the restoration of the Pieta!

The Alma King – repaired. The specimen now sits in the Denver Museum of Natural History.

There is little argument that the repair of the Sweet Home rhodochrosites was the right course of action, and certainly did not diminish the value of the specimens. However, it also coincided with the crest of a darker tsunami in the collecting hobby that demanded specimen perfection, and art aesthetics overtaking all other metrics of mineral specimen evaluation. A significant percentage of the Sweet Home specimens required repair, although the evolving euphemism was “specimen preparation”; a dialog developed around the theme of “returning the specimen to the condition it was in nature”. This catch phrase has become the a divide between collectors; those that prize the art of mineral specimens are willing to see flaws removed by polish and resins, while other collectors recoil at any man-induced enhancements and celebrate only that which can be documented “as found”. This gulf is wide, and brings cries of “fake and fraud” from collectors in the later group when they view many of the world’s best mineral specimens. However, this group of collectors – the old school – is dying away. Not yet irrelevant, but mostly marginalized. I am old school.

The cover of the Mineralogical Record, January 2015. On the cover is one of the most amazing tourmaline specimens in existence, and the volume is full of information on the Pederneira mine. What is missing is the painstaking history of specimen repair and restoration – much work is done with added materials.

When a grey line becomes red — and crossed

In the last 50 years the mineral collecting hobby has seen dramatic changes – or perhaps evolution. What was once the realm of rockhounds is now a glided age of art. One of the most obvious symptoms of this change is what collectors accept and expect in a mineral specimen. Repair and restoration have always been important for mineral specimens; however, the definition of repair and restore has changed as prices have escalated. There has always been a desire to make specimens attractive, but today it is expected that many specimens are oiled, waxed or sprayed with silicon to enhance their luster and hide their imperfections. Use of these cosmetic trappings was once a “red line” for collectors – absolutely rejected. But just like US foreign policy on the use of chemical weapons, that red line was faded to grey. A tour through the many hotel rooms of the “high end” mineral dealers participating in the 2015 Westward Look Fine Mineral Show in Tucson (February 6-8) reinforces this dramatic shift; it is fair to say that most expensive fluorite specimens for sale have been treated with oil, every recent amazonite dug from the pegmatites in the high peaks of Colorado has been “juiced” to enhance the luster, and most gem-quality garnets are getting at least a spray of enhancement. And, further, casual conversation with collectors seems to reinforce that this is what they want. Perfection is essential for a work of art.

A comparison of “before and after” for a cut emerald. The cut stone on the left is natural, and on the right has been treated with cedar oil (from http://www.jfjco.com/2014/05/18/emerald-treatments/)

The desire to “improve” minerals is a couple of thousand years old. There is written accounts of Greeks using cedar oil on emeralds to enhance the color. The purpose of the oil was to fill the flaws and cracks with a material (the oil) such that when light is shined on the crystal there would not be reflections from the imperfections. The cedar oil had approximately the right index of refraction (about the same as the emerald itself), and low enough viscosity (when heated) to flow into the tiny cracks, but high enough such that it would remain (at least for a while) after treatment. Today the oil is mixed with a polymer which “fixes” the oil. There are about a half dozen “restoration” labs in the US that work on minerals, and most have proprietary processes to do essentially the same thing as the cedar oil treatment except for fluorite, sphalerite, garnet, etc. The science behind these processes is fairly sophisticated — but the treatment is rarely disclosed.

Classic Gary Larson cartoon – Rowing in Circles. This reminds me of specimen restoration – dealers on one side, collectors on the other. Dealers provide what collectors want, and collectors hear from dealers what specimen perfection should be. It is just rowing in circles.

Today it is hard to “lay blame” for the practice of mineral restoration that relies on removing perceived imperfections at the doorstep of dealers. The nature of the “trophy collector” is to find perfection – and that sense of perfection does not have to be the hand that nature dealt. Further, it is clear that repair and restoration no longer decrease specimen value, but actually increase value. As Sir Walter Scott opined: Oh what a tangled web we weave, When first we practice to deceive.

Old School with a New World Order

I love collecting minerals – it is something that I have done with passion for more than 50 years. I have changed along the way, and the hobby has changed even more than I. I am deeply disturbed by many of the changes, but that does not make them “wrong”. Just as I am aghast at at what I perceive as the personal values of generations other than mine, my sense of why I collect, and what a mineral specimen means to me, does not have to be shared with others. The Dalai Lama says: “Happiness is not something ready made. It comes from your own actions.” I don’t need to change what and how I collect. It is the science and human story that are codified and crystallized in my minerals. That is why I happily collect that which is repaired and total reject oils and waxes. A red line.

Seeing Red: The Addictive Allure of Proustite

Beauty of whatever kind, in its supreme development, invariably excites the sensitive soul to tears, Edgar Allan Poe, 19^th century American Poet.

Proustite, Chanarcillo, Chile (3.8 cm tall). Wendell Wilson photograph. This is the first very fine proustite I obtained for my collection in 1983 from Simon Harrison. Click on photographs to get full-size versions.

There are certain minerals that hypnotize the collector – some with their monetary value, some with their art esthetics, and others with their specimen fame and history. A few appeal to a most primal attraction, a fascination with a rich and distinctive color. Perhaps no species in the mineral kingdom has a more unique and appealing hue and chroma than proustite; vermillion-scarlet red, appearing to glow under moderately bright light, yet fleeting and fading with time. In Mexico and Chile, miners use the phrase “Sangre de Toro” – the Blood of the Bull – when they encounter freshly broken rock that exposes proustite (or the closely related mineral pyargyrite). These miners celebrated the rock bleeding with rich silver ore.

A “great proustite” is prized in any mineral cabinet, and is considered an essential in a great mineral collection. However, proustite is enigma to most collectors — beautiful, but it poses very special challenges in terms of curation. Proustite is well known to darken on exposure to light – mainly sunlight, but also on exposure to the light from most electrical bulbs found in mineral cases. Proustite is probably the only mineral that is proudly advertised as “stored away in a dark box for the last 100 years”. A great mineral that no one every gets to observe? By far, proustite is the mineral I get questioned must intensely about; Can you reverse the darkening? Why does my proustite that I leave boxed up develop a white coating? Can I find display glass for my mineral case that will block damaging light? Unfortunately, the same chemistry and physics that endows the mesmerizing color to proustite leads to its ultimate demise.

I bought my first fine proustite in 1983 at the Tucson Gem and Mineral Show — or more correctly, I bought it late one evening in a dingy hotel room in the Desert Inn located a few blocks west of the TGMS show. The crystal is about 3.8 cm high, and distinctive in its habit; there is no question that it was from Chanarcillo, Chile. I was introduced to an English mineral dealer named Simon Harrison, who was reported to have a fine proustite. Simon took me into the bathroom to show me the piece — I recall that the bathtub was filled with ice and cans of beer, and there were mineral flats stacked high — and as I opened the box I was incredibly excited (the crystal is shown at the top of this article). Inside was a perfect prismatic crystal, fantastic color, and an retired British Museum of Natural History label. Reality splashed over me as I realized this piece was probably out of my meager means — having just completed my PhD, and was only notionally visualizing what a “paycheck” was. He told me the price was 3000 dollars – cash, no stink’in checks. I quickly said yes, but had no clue where I was going to find 3k. I had three flats of pretty good material in my car out front, and I hoped to sell them in the next couple of days. I was incredibly lucky that I was able to cajole a dealer to take them all for 3,800 dollars, and I became the proud owner of a piece of ruby silver.

Labels from the Chilean proustite pictured above. The label on the left is from the British Museum of Natural History, and documents that the specimen was purchased in 1865 from Steve’s Sales Room.

I showed my treasure to a number of friends and colleagues and the everyone told me it was great, but that I had to keep it closed up tight in a box, and make sure it never saw the harsh and bright Tucson sunlight (I recall thinking that perhaps everyone was confusing the proustite with a miniature vampire…). I stored it away, and was happy. Two years later I opened up the box to show a friend, and I was dismayed to see a white powder near the base of the crystal. The color seemed as great as ever, but what the heck was the white powder, and what did it portend for the demise of my great specimen? I removed the white powder with a tooth brush and x-rayed it; I found it was arsenic oxide. This seemed mysterious to me, and started me down a path of understanding the complex chemistry and physics of proustite.

Since that first purchase long ago, I have added about 15 proustites to my collection. I love the species, and even occasionally show the pieces. I have also probably been asked a hundred times on how to reverse the aging of proustite; sadly, just like the human body, a grand chemistry experiment is going on all the time, and although it is possible to delay the darkening of the crystal, the majestic color will eventually change. It is not a mystery, but a testament to the wonderful properties of the element silver.

Proustite crystal, 3.1 cm high, Schneeberg, Germanay. This piece is reported to be from Shaft 207, and was probably mined in the 1950s. Jesse La Plante photograph

The next two sections of this post are about the structure and color of proustite – they require some faith in quantum mechanics, and for some readers it is best to just jump to the section on The World’s Great Proustite Localities.

The structure of proustite; silver sulfides and sulfosalts all die and go to heaven

The color of proustite, and the fact that it fades and decomposes on exposure to sunlight, is a result of its chemistry and crystal structure. The chemical formula for proustite is Ag₃AsS₃, which represents the arsenic end-member of a solid solution series with the “dark ruby silver” pyrargyrite (Ag₃SbS₃). From a chemical point of view, the proustite-pyrargyrite series is one of the simplest silver-bearing sulfosalt systems. “Simple,” however, is relative when dealing with anything that contains silver. For example, in the laboratory it is possible to make antimony-rich proustite; yet in natural proustite, only a tiny fraction of the arsenic is actually replaced by antimony.

Crystal structure of proustite; shown on the left is the unit cell and in the center is the packing of molecules in a typical crystal shape. Most proustite crystals are prismatic terminated by the scalenohedron and the obtuse rhombohedron.

The crystal structure of proustite contains covalently bonded As-S₃ pyramids, which are stacked in a spiral parallel to the c-axis of the crystal. The silver atoms are situated between the As-S₃ pyramids, and link the over and underlying pyramids via S-Ag-S bonds. The figure above shows the packing, and the resulting crystal symmetry. The stack of the unit cells gives a hexagonal structure (in the ditrigonal pyramidal class). Proustite crystals are typically highly modified scalenohedrons – often they resemble “dog-tooth” calcite crystals.

Prismatic proustite crystals, St. Andresberg, Harz, Germany. The cluster of crystals is 1.6 cm across. Jesse La Plante photograph.

The classical representation of the atomic interactions in the unit cell does not capture the complexity of proustite very well; it is important to take a quantum view, more fully appreciating that the silver atoms are fickle with their attachment to a given sulfur atom. Below is an individual proustite molecule presented using Einstein’s model for the harmonic displacement of atoms. The ellipsoids represent an envelope of space with a certain probability that the atom is inside; in the figure sulfur is shown in yellow, arsenic in green, and silver is the in silver (of course!). The silver atoms have the largest ellipsoids — in fact, larger than the entire As-S₃ pyramid dimension — reflecting the fact that silver wanders within the structure.

Einstein’s model for the harmonic displacement of the atoms within a proustite molecule. The sulfur atoms are shown as yellow and arsenic as green, and the silver atoms are the large ellipse on the outside. This figure was made by Robert Downs, UofA mineralogist, a structural guru.

In the classical description of the proustite structure a given silver atom interacts with two sulfur atoms (on the over and underlying As-S₃ pyramid). However, if you consider the interactions of a given Ag atom with the neighboring six sulfur atoms, it is possible to define a very distorted AgS6 octahedral group.

Interaction of silver atoms in proustite with neighboring sulfurs. On the left image, there are two bonds which are vertical and the four non-bonded S are in the horizontal plane. In the right image, the view is down the direction of the vertical bonds; the image shows the flat pancake shaped displacement ellipsoid which “cages” the silver. Figure courtesy of Bob Downs.

In this representation two of the S atoms are much closer to the silver atom as compared to the other four (making the silver 2-coordinated). The other 4 sulfur atoms form a plane around the Ag, defining a “cage”. When the silver atom experiences thermal motion it bounces back and forth between the four sulfur atoms undergoing short periods of being bonded to each of them. This can lead to strong silver migration within the proustite structure — and this is the root cause of the deterioration of proustite on exposure to light!

Figure from the 19th century showing the growth of silver wires from proustite crystals. These wires were produced by spot heating — and look very much like the silver wires from acanthite.

The mobility of silver in sulfides and sulfosalts is described as a thermal effect, which usually leads one to the conclusion that physical heating is required. In fact, the thermal motion of the silver atoms can be excited by radiation, including visible light. When light shines on proustite the unit cell increases in volume; this volume is accommodated in the c lattice parameter, meaning that the distance between the As-S₃ pyramids in adjacent layers increases, promoting a reaction that liberates the arsenic which reacts with the atmosphere to produce As₂O₃ – the white powder that is sometimes seen on proustite. The light also mobilizes the silver, which typically combines with the sulfur to form acanthite. The “darkening” of proustite on exposure to light is actually the surface growth of acanthite and silver.

Proustite cluster from Schneeberg. Specimen is 3.1 cm across. There are a number of silver outgrowths on the proustite. Jesse La Plante photograph.

The chemical changes associated with light degradation of proustite are irreversible. Once the silver migrates and reforms on the surface as a new sulfide, the host proustite is forever changed. The “darkening” of the proustite is in fact a surface coating, and it can be removed with silver cleaner, although this “cleaning” leaves a pitted and damaged surface.

The mobility of silver in proustite is hardly unique; in fact, all silver sulfides and sulfosalts are temperature sensitive. The classic example is the growth of silver wires out of acanthite. Recently, there have been a large number of “constructed” silver wire specimens from Morocco and China where acanthite crystals have been blow-touched to liberate bright curls of silver. The same thing happens to proustite when point heated, something that has been know since the 19th century when the figure above was published (criminal, blow-touching a proustite crystal!).

The color red – band gaps

The structure of proustite is also responsible for its marvelous color. It also requires a detour through quantum mechanics to understand how electrons behave with energized. Proustite is a semiconductor, and thus its color is controlled by the energy of electrons and the “band theory of metals”. The main tenet of band theory is that the outermost electrons of the atoms within the mineral belong to the crystal as a whole. For pure metals, such as silver and gold, each atom contributes the electrons in their outer orbits to a “pool”; these electrons are free to move throughout the crystal, and this results in high thermal and electrical conductivity, and metallic luster. For semiconductors – like proustite – there is a prevalence of covalent bonding, or electron sharing. This limits the mobility of electrons, and there are gaps in energy between the covalence band and a band that would be required for the true electronic sharing (the conduction band). The size of this energy gap controls the color of the semi-conductor.

Energy gaps, or bands, in minerals and metals. If the gap is nonexistence, there is no band, and the material behaves as a conductor. If the gap is small, the material is a semi-conductor. The size of the gap controls the perceived color of the material.

For metals, the electron pool absorbs energy from incident light and the electrons are excited to higher energy levels; the electrons return to their native lower energy state and emit a photon of energy proportional to the difference between the excited and native levels. For gold, the electrons have a strong absorption of energy at 2.3 eV, which we observe as yellow. For silver, the absorption peak is at about 4 eV, which is closer to the ultraviolet – so all the visible spectra is returned and the metal acts like a mirror. Hence the shiny, nearly white color of the metal.

Color table for semi-conductors. The visible light spectrum covers a range of energies, and absorption is possible at all energies above the band-gap of the material, but not below. If the gap is very small (<1.5 eV) then all the light energies are absorbed and a black color is observed.

For semiconductors, it is only possible to absorb the energies of incident light at all energies above the band gap, but not below. If the gap is very small, the color appears black. If the gap is very large, no absorption occurs, and the mineral appears colorless. Diamond has an energy gap of 5.5 eV, well beyond the spectra of visible light. Proustite has an intermediate gap – about 2 eV — and therefore only red light is transmitted; all other colors have energies larger than E_g and thus, are absorbed. Pyrargyrite has slightly smaller gap (the difference between a covalent bond with antimony vs arsenic) and therefore is slightly darker.

The unique hue of proustite is a product of silver-sulfur bonds competing with the arsenic-sulfide pyramids. Since most silver sulfides and sulfosalts are similarly constructed, they all have a red color. We tend to think of minerals like miargyrite and polybasite as “black”, but in fact their streak is red.

The World’s Great Proustite Localities

Proustite is known from thousands of localities, but only a paltry half dozen have produce collector specimens of note. Proustite and pyrargyrite are generally late forming minerals in hypogene (high temperature and pressure fluids) environments, although occasionally there found in supergene (near surface, and typically controlled by meteoric waters) environments. Proustite is considerably rarer than pyrargyrite; both minerals are typically dispersed in smallish grains within vein systems. The abundance of proustite in world-wide silver localities portends that there should be exceptional crystals from many localities. However, macro-crystals are quite rare except at Chanarcillo, Chile and near Schneeberg, Germany.

Chanarcillo: The undisputed heavy weight champion of proustite localities is Chanarcillo, Chile. Between 1850 and 1875 an extraordinary number of terminated, undamaged proustites were recovered in veins of calcite. The largest of these crystals is reported to be more than 9 cm in length, and hundreds of specimens are known in museums and private collections across the globe that are long prismatic candles of red in excess of 5 cm length.

Proustite, Chanarcillo, Chile. This specimen was originally in the Vaux collection, and is now in the National Collection at the Smithsonian Institution. The main crystal is a little longer than 7 cm. Photograph provided by Paul Powhat.

The Chanarcillo deposits are located south of Copiapo, about halfway between Antofagasta and Santiago, Chile, in the Atacama Desert. In May 1832 a freight hauler and prospector named Juan Godoy was hunting Ilamas when he tired and decided to rest under the shade of an outcrop. Godoy noticed a waxy vein and began to pry the vein material out with his knife – he later described it as “soft as cheese”. He loaded up two mules with the ore — chlorargyrite — and headed to the nearby town of Copiapo to have it assayed. Godoy entered into partnership with a friend, Juan Callejos Miguel Gallo, and founded the Descubridora mine. Rumors of the richness of the strike started a rush to Chanarcillo, and by 1850 there were 1,750 mires in the district. Unfortunately, the story of Godoy ends sadly, in the way of many prospectors; Miguel Gallo became immensely wealthy, but Godoy squandered his share of the Descubridora and died a beggar.

Vaux proustite, National Collection, Smithsonian Institution. This specimen, thought to be from the Dolores Mine, is about 4 cm high, and cherry red. The photo was taken by Wendell Wilson in 1972 – at the very beginning of his illustrious career as a mineral artist, photographer, scholar, and editor.

The Descubridora Mine produced the largest and best native silver specimens from Chanarcillo. Much of the silver occurred as thick wires encased in calcite, but the most characteristic habit is arborescent “flags” or herringbone plates of crystals. Two other mines produced specimens of note: the Mina Dolores Tercera and the Bolados. The Dolores is perhaps the most famous to mineral collectors, and during the 1850s the lower levels of the mine encountered a series of vugs filled with proustite, acanthite and chlorargyrite. The Bolados (named after four brothers who discovered it) contained huge masses of native silver — one of these weighed an estimated 1,360 kilograms, and had to be hand-chiseled from the mine because black powder blasts only dented and bent the lode. Another Bolados bonaza pocket contained chloragyrite and silver weighing 20,450 kilograms!

Chlorargyrite from Chanarcillo, Chile, about 6 cm across. I obtained this from Cal Graeber in 1999, and although it is just labeled as “Chanarcillo”, the date of the original label and form suggests it was from the Bolados Mine.

There were 18 major mines in Chanarcillo that produced more than $90 million (as measured in 1875 dollars) worth of silver in aggregate. Most mining was abandoned by the end of the nineteenth century due to the exhausting of the ore. There were periodic attempts to revive the camp in the camp in the 20th century, but this only resulted in all the dumps being hauled away for processing. Every trace of mineralization has been chipped away from the tunnels and open workings. I visited Chanarcillo in 2001, and was amazed how little remained. The value of the proustite is not lost on the locals; if you travel to Copiapo and inquire about buying proustite, someone will show up at your hotel room with red-colored rock and asking price of thousands of dollars. Sadly, no new proustite has been recovered in more than a century.

Fettelite crystal group, Chanarcillo, Chile. The largest crystals are 0.7 cm across. Jesse La Plante photograph.

However, there are plenty of Chanarcillo proustites stored away in museums, and occasionally returned to the collector world. About 12 years ago a large proustite was traded out of the Harvard Museum; as traded it was an ugly clod. It was a mass of calcite with glimmers of proustite. The dealer made the trade with the hope that the removal of the calcite would reveal a masterpiece. In fact, it revealed many masterpieces! During the cleaning it also revealed some material that looked like red mica. Testing confirmed it was fettelite, a rare silver-mercury sulfosalt (Ag₁₆HgAs₄S₁₅). Fettelite was only described in 1994, and all the known material was flakes less than .2 mm across. However, the “cleaned” Harvard piece yielded crystal books to .7 cm! I was fortunate to acquire the very best of these (before others decided that these should be really expensive since they were the world’s best!).

Proustite, Schlema, Germany. Specimen height is 5.0 cm tall. Jesse La Plante photograph.

Schneeberg/Schlema: The Erzgebirge — translates as the ore mountains – is a fault block mountain range that forms the border between southeastern Germany and the Czech Republic. For mineral collectors, The Erzgebirge is a mineral locality of mythical proportions; Freiberg, Marienberg, Annaberg, Jachymov, Johanngeorgenstadt, Pöhla and Schneeberg. These mines operated for centuries, and gave birth to modern mining geology, engineering and mineralogy. These mines produced a larger volume of world class silver minerals than any where else on the globe – and so many of these specimens are preserved because of the rise of gentlemen naturalist that were ravenous collectors in the 18th century had access to these marvels.

The “silver road” – a journey through the most amazing silver mineral localities in the world. The yellow line traces the route from Dresden to Schneeberg. I had the privilege to make this pilgrimage in 1991, shortly after the fall of the Berlin Wall.

Proustite is found throughout the Erzgebirge, but a series of mines in the Schlema valley produced the very best specimens. The town of Schneeberg sits at the western end of a small valley — about 5 km long — that drains into the Zwickau Mulde (river). Within this modest strip of land sits the Schlema-Hartenstein and Schneeberg mining districts. Silver was known to have been mined in the area from at least since the beginning of the 15th century, and the first major discovery occurred in 1470. Within 4 years there were 176 mines recorded to be producing silver. The most famous of the early mines was the St. Georg; in 1477 a large lode of native silver and various silver sulfides was discovered which is said to have contained 20,000 kg of silver. A large slice of this lode exists today in the Senckenberg Natural History Collections, in Dresden.

A piece of the 20,000 kg silver lode discovered in 1477 in the St. Georg mine in Schneeberg. Photograph by Barbara Bastian.

The mines in the Schneeberg-Schlema area exploit a network of hundreds of veins that vary in size; the most important are over 2 km in length and 3 meters wide. The character of the mineralization within in the veins is complex which is the result of the superposition of multiple hydrothermal events over a long period of time — from the Permian to the Cretaceous. The complex mineralogy is characterized by the metals C0-Ni-Bi-Ag-U. In fact, the variety of metals also explains the long mining history of the region. Within 25 years of the first major discovery most of the silver mining had ended, but the region was revitalized in 1520 when cobalt became an important commodity to produce blue glass. In the early part of the 19th century the focus of the mining shifted to nickel, and by 1830 the uranium became a main mining target.

Proustite, Schneeberg, Germany. Crystal 2.7 cm tall. Jesse La Plante photograph.

After the conclusion of World War II the Soviets invested heavily in the region to mine uranium for their nascent nuclear weapons program. By the end of the 1950s East Germany was the fourth largest producer of uranium, and the Schneeberg-Schlema area is now recognized as the largest vein-style uranium deposit in the world. By the time the mines shut down in 1990 the total uranium production was more than 96,000 tonnes.

Waste dumps from the mining of uranium above Schlema. Photo was taken in 1960 (from the German government agency responsible for remediation).

Although the Schneeberg-Schlema mines had a complicated history in terms of the target metal, a constant through time was the occasional encounter with rich pods of silver ore. Proustite specimens were documented as being recovered from the mines for over 500 years. Many of the best specimens were recovered in the 20^th century, and preserved. Unfortunately, the names of the specific mines are often obscured — in fine Soviet tradition the mines operated post WWII were donated by numbers assigned to the adits or shafts. The most famous of these shafts was “207” located in Niederschlema. WISMUT, the uranium mining enterprise, made a gift of several dozen stunning proustites from shaft 207 to the Technische Universität Bergakademie Freiberg (the Frieberg Mining Academy). These proustites reside in a drawer – hidden from light, but when the proustite drawer is brought out the reaction from collectors is always one of disbelief!

Proustite, Schneeberg, Germany. Crystal height is 3.2 cm. Jesse La Plante photograph.

To Show or Not to Show

Proustite is a marvelous and complex mineral – to quote Winston Churchill, it is “a riddle, wrapped in a mystery, inside an enigma”. The unique color of proustite demands attention, but each flash of attention under the display lights inevitably permanently changes the specimen. There is no simple solution to delaying the darkening of proustite — the short wavelength end of the spectra causes the reaction to occur more rapidly, but the lattice will swell with exposure to any part of the visible light spectra. Thus, it is not possible to just install UV glass on a mineral case and assume your fine proustites will glow red for a generation. On the other hand, a brief exposure to light for an occasional display has little consequence. Judicious displays — both in frequency and out of direct sunlight – can make poustites objects to behold for at least a hundred years.

Tales from the Tags: Mineral Labels and Specimen Value

I go down to Speaker’s Corner I’m thunderstruck They got free speech, tourists, police in trucks Two men say they’re Jesus one of them must be wrong – Dire Straits, 1982 song Industrial Disease

Chalcopyrite coating acanthite Joachimstal, Bohemia (now in the Czech Republic). Originally in the A.F. Holden Collection, bequeathed to the Harvard Mineral Museum, traded out and sold to William Pinch, and eventually came to my collection from dealer Cal Graeber.

One of the questions I get asked most often when I visit a mineral show: “Is it real?”. I mean this in a mineralogical sense, not a judgement of my personality. The origin of the question is uncertainty about a mineral sample, and the particular inquiry is focused on whether the mineral is as advertised, or “fake”. The nature of fakery in the mineral hobby can be subdivided into four broad categories: (1) is the mineral actually identified correctly, (2) has the mineral specimen been enhanced, repaired or constructed, (3) is the mineral actually natural, and (4) is the ancillary information with the specimen – locality information, previous ownership, etc. – correct? To me, the last category is particularly vexing. The ancillary information, usually provided in a label or series of labels associated with a specimen, documents the history and significance of the specimen. I collect minerals partially because of the their “science” (chemistry, geology, and crystal beauty), but also because they are artifacts of history. Someone had to mine the specimen, decide it was worth keeping, pass it on to a collector or dealer that valued it, and finally making its way to my collection. From underground mine to my collection the specimen develops a patina of human history. I very much value this history — the story in the label with the mineral is part of its “worth”. The specimen pictured above is an exemplar of a mineral as a historical artifact. The specimen is a miniature sized matrix acanthite with an epitaxial coating of chalcopyrite. The locality is Joachimsthal, one of the most important historic silver mining regions in the world. The specimen has a well documented pedigree: it was in the A.F. Holden collection that was bequeathed to the Harvard Mineral Museum in 1913, and transformed Harvard’s collection from a typical university cabinet into one of the world’s greatest mineral holdings.

Labels for the chalcopyrite coating acanthite specimen pictured at the top of the article. The specimen was in the A.F. Holden collection, went to Harvard, traded to a dealer that sold it William Pinch. Eventually, Pinch sold the piece and it made its way to my collection in the 1990s.

In 1912 the Engineering and Mining Journal declared that the finest collection of minerals in the United States is “believed to be that in the American Musuem of Natural History in New York, the basis of which was the famous Bement collection. There are several important private collections. Among those, that of Col. W.A. Roebling, Trenton, N.J., is considered to be the best; anyway, the largest. Next in rank are probably the collections of A.F. Holden, Cleveland, Ohio and Fred Canfield, Dover, N.J.” Albert F. Holden graduated from Harvard in 1888 with a degree in Mining Engineering. After graduation, Holden entered the family mining business, and by 1906 he had built one of the largest mining and refining companies in the world. His holdings included what would become the Bingham Canyon copper mine in Utah, and dozens of mines spanning the mineral wealth of Alaska to Mexico. In the 1912-13 Annual Report on Harvard University, the curator of the Mineral Museum, John Wolff, wrote “received this year a mineral collection which represents the greatest single gift of minerals made during its history of one hundred and twenty years…Mr. Holden had found time in the last eighteen years to accumulate one of the finest private collections in existence….As a result, the larger part of the six thousand specimens are of the highest quality, while many are unique.” In the detailed instructions to Harvard accompanying the collection, Holden wrote “There shall be no obligation on the Museum authorities to keep any of the specimens when they have lost their scientific interest”. Although the chalcopyrite coating acanthite in my collection is modest, its tie to a mining great, and subsequent membership in the Harvard Museum, and ultimately its pathway into one of the great modern collectors, Bill Pinch, is what makes it “more” than a pretty mineral. Remove the labels, and the specimen is interesting, but it loses its significance. The tale told of specimens from labels is their character — and it is also why labels can also be used to deceive or misrepresent.

Acanthite mounted on a wood pedestal from Bryn Mawr.

The original mineral twitter: Mineral Labels

I am often surprised that many mineral collectors don’t spend much intellectual capital on the pedigree of the specimens that they pursue and collect. That statement is, of course, a gross generalization because there are many collectors that intensely focus on the specimen history, but most collectors are first and foremost interested in the perfection of the specimen itself. However, every specimen has a story to tell, and often that story is gleaned from a few lines written on an old mineral label. Although labels may only contain the briefest inscriptions, these are often delightful clues to the thoughts and passions of the original collector. The picture above is a large thumbnail of acanthite from the Las Chispas Mine, Arizpe, Mexico. For a very brief period, the first decade of the 20th century, the Las Chispas mine near Arizpe in Sonora produced some of Mexico’s largest and best specimens of polybasite crystals, large clusters of “poker chip” stephanite crystals, fine acanthite crystal clusters and a few very fine pyrargyrite specimens. Many of the specimens were saved through the enlightened efforts of mine manager Edward L. Dufourcq (1870-1919), and now populate museums and privates collections worldwide. The pictured specimen is fairly unremarkable, even if distinctive of Las Chispas acanthites. However, the label (and the wood stand that holds that displays the specimen) are what make this a historical artifact. I purchased this specimen from a dealer in 1986 – but what I saw when it was displayed in his stock was the label — it is a very distinctive “Vaux” tag! George Vaux (1863-1927) was an attorney and member of one of the most important Pennsylvanian families – in fact, he was the 9^th George Vaux (and passed the name on to his son too!). George Vaux was the nephew of William S. Vaux, who one of the earliest American mineral collectors. George followed his uncle’s lead and passionately collected minerals. When he died in 1927 he had amassed an amazing collection, particularly rich in South American and Mexican specimens (Vaux’s Chanarcillo proustites are still considered some of the finest examples of what I believe is the most beautiful mineral). Vaux lived in Bryn Mawr, located west of Philadelphia, and upon his death his family kept the collection intact and on display in their home. Bryn Mawr is home to the small college of the same name, founded by the Religious Society of Friends (Quakers) in 1885. In 1958 the family decided to donate his collection of more than 8,000 specimens to the college – and suddenly a small women’s liberal arts college had a major mineral holding! The transfer of the collection included Vaux’s labels – there are several types, but several thousand were the simple lined cards, with handwritten descriptions (like the one pictured above). In the early 1980s many of the Vaux specimens were traded out of the Bryn Mawr collection, including my acanthite. The wood stand and black wax mount were Vaux’s work. On the base of the stand Vaux wrote “Cahn, 11/20” which indicated that he had bought the specimen from Lazard Cahn, a Colorado Spring mineral dealer. Eventually, it was acquired by Al McGinnis (a San Mateo dealer) for his private collection, which was dispersed upon his death. A few years after I acquired the Arizpe acanthite, I found another Vaux labeled acanthite specimen in the stock of mineral dealer Gene Schlepp. In fact, the Vaux label was was tagged with the number 703, only a few digits different than the Arizpe piece!

Aguilarite, Guanajuato, Mexico.

The Vaux label stated that the specimen was Argentite (acanthite) from Guanajuato, but I suspected the specimen was actually Aguilarite (Ag₄SeS), a far rarer mineral. The skeletal dodecahedrons are distinctive of the species, and the specimen looked very much like the very best aguilarites I had seen in other collections. I purchased the piece, and hurried off to the lab to do an x-ray. My hopes were confirmed – a outstanding aguilarite with history to boot!

Vaux label

The front of the Vaux labels only tells part of the story. Turn over a Vaux label and there is a few scribbles that connect Vaux to his mineral suppliers. Below is a picture of the Arizpe and Guanajuato labels. In Vaux’s hand writing you can see where and when he acquired the specimens. The Aguilarite was obtained from Wards in 1895 — which is very consistent with the very best samples were mined. Around 1890, Ponciano Aguilar, superintendent of the San Carlos mine at Guanajato collected an “unknown” that he thought might be Naumannite, and sent it to S.L Penfield for identification — and Penfield discovered it was a new mineral and named it in honor of Aguilar.

Back of the Vaux labels; where the specimen was purchased, when it was purchased, and a three letter code. The code is likely the purchase price.

A mystery on the Vaux labels are the three letters scribbled after the date of purchase. I have looked at about a dozen Vaux labels and they always have these initials, all different. Wendell Wilson, editor of the Mineralogical Record, suggested that this might actually be an encrypted purchase price. Several collectors from the first half of the 20th century used ciphers to record value. Martin Ehrmann used “tourmaline” as his cipher — 10, non-repeating letters, each corresponding to a numeral, 1-9 and 0 (e.g. tne would translate to 190). Carl Bosch, whose fabulous collection ended up in the Smithsonian Institution, used a similar code, with amblygonit thought to be the cipher used to record value in German Marks. I don’t have access to nearly enough of the Vaux labels to “break the code”, but it is likely that the three letters are some important secret about the specimens. Not all minerals come with a rich history, and when there is a documented pedigree it is still hard to convert that history to a monetary value. The Vaux labeled specimens in my collection are cherished by me, but in the future (hopefully distant future) when they are sold to other collectors the value will be mostly determined by comparison of the specimens with “their peers”. The aguilarite will still be one of the best in the world, with or without the label. But the real value will be the story behind the minerals – it may not be monetary value, but it will be fingerprints of humanity on stones recovered from the Earth.

Bideauxite, Tiger, Arizona

When Labels Go Bad

One of specimens I treasure the most in my collection is a Bideauxite, a very rare lead-silver chloride (Pb2AgCl3(F, OH)2) from Mammoth-St. Anthony Mine, Tiger, Arizona. The photograph above is a closeup of my specimen, and displays two hexoctahedral crystals of Bideauxite associated with boleite on a quartz matrix — the crystals are tiny, only a few mm across. The unusual chemistry of Bideauxite requires a very restrictive set of conditions for formation, and in fact, the mineral is only documented to come from two localities: Tiger and a small prospect in Tarapaca, Iquique Province, in northern Chile. The species is named after the late Richard Bideaux, a good friend and a fountain of knowledge for all things mineralogy (he is co-author of the Handbook of Mineralogy), especially Arizona mineralogy (co-author of Mineralogy of Arizona). Richard “discovered” the mineral when working on his thesis at Harvard; he was going through material in the Harvard Mineral Museum from Tiger and found a tiny gray-pink fragments of a mineral he thought was chlorargyrite on boleite. Richard sent the material to Sid Williams who determined that it was a new mineral, and named it Bideauxite. In 2005, Dave Bunk bought part of the mineral collection that contained many specimens from Erberto Tealdi (the late editor of Rivista Mineralogica Italiana) collection. Tealdi collected a large suite of minerals from Colorado — and in the material Dave acquired was the most amazingly labeled sample: Bideauxite, Sherman Tunnel, Leadville, Colorado. Acquired, Rich Kosnar. Looking at the sample I immediately knew that it likely Bideauxite, but what a bizarre reference to the Sherman Tunnel! Never has there been a more ridiculous assertion for a locality — wrong geology, wrong mineralogy, and about as believable as the theory that Roman Christians established a colony on the outskirts of Tucson, Arizona around 700 AD (this theory is based on an archeology hoax, but will live forever on the internet – I love archeological hoaxes!). It is clear that the original label listing the Leadville locality was used to deceive, but really it was a rather flaccid attempt. I eventually obtained the Bideauxite from Dave Bunk, and have labeled it as from “Tiger.” This is an example of a very troubling phenomena in which the Label is Bad. In the case of the Bideauxite, the bad label has little consequence because it was so preposterous. However, for the very reason that labels add to the value of specimens — both in terms of history and monetary value — the issue of bad labels is one of the worst diseases in the mineral collecting hobby.

The Colorado Dragon

Recently, Pala Minerals published an article about the sale of arguably the most important Colorado mineral specimen — a gold sample from the early days of the Colorado’s rich mining history — in their internet newsletter (http://www.palaminerals.com/news_2014_v2.php). The specimen is fabulous – more than 5 ounces of crystallized gold that demands attention. The specimen is reputed to be from the Gregory Lode, Gregory Gulch, Gilpin County, Colorado – the label is shown below. The significance of the label is “Gregory” — as in John H. Gregory. Gregory, a prospector from Georgia, is credited with discovering the first major Colorado gold deposit located near what would become Central City, in May, 1859. Gregory sold his claims, and pretty much disappeared (although there are many Gregory legends, mostly they are unsubstantiated canard). The label changes the “Colorado Dragon” from a great mineral specimen and transforms it to a hugely signifiant historical artifact. Further, the mineral label states that the gold actually belonged to John Gregory, and that he had personally donated the treasure. There is absolutely no other evidence that Gregory collected or owned this outstanding gold, nor that he donated specimens, but the label titillates!

Label included with the Colorado Dragon. Note that it states Gregory donated this gold, even though he disappeared in the early 1860s.

The “original label” for the Colorado Dragon is stated to be from the State Historical Society. The State Historical Society received minerals originally acquired by the Colorado Bureau of Mines over a period of about 80 years, in 1956. This mineral collection was filled with history – it had specimens from senators, miners, and millionaires. The label above serves as exculpatory evidence for those that would cast doubt on the provenance of the gold. The faded piece of paper with a few typed phrases links the nugget with the birth of the Centennial State.

A label accompanying the Colorado Dragon, from the Colorado School of Mines

Eventually, the Historical Society gave the mineral specimens to the Colorado School of Mines, and it was placed into the Mineral Museum holdings. The photo of the label above is stated to be the School of Mines tag associated with the specimen. In 1990s the Colorado Dragon was obtained by Colorado Dealer Richard Kosnar (the same Kosnar associated with my bideauxite) from the School of Mines. This year the specimen was obtained by George Hickox a noted Colorado gold collector. This would be a remarkable tale, but just as the labels add immeasurable value to the gold, they also cast a dark cloud over the authenticity of the specimen. The problem is that there are at least two more specimens labeled “number 5600” – so three competitors to the throne! Two of the specimens are labels EXACTLY the same (reference to donation by Gregory, which is certifiably false) including the Colorado Dragon! Just as the tag line at the top of the blog from the Dire Straits’ song says that when two people claim to be Jesus, one must be wrong! In the case of the Gregory Gulch gold there are three competitors for the label designated 5600.

Number 5600 in the Colorado School of Mines display. Note no mention of a donation by Gregory.

The photograph above shows a gold specimen on display at the Colorado School of Mines, and it carries the number 5600. This specimen has all the documentation to suggest that it is the original 5600, although no where is there any indication that it was donated by the original prospector. This does not mean the specimen on display is authentic. There are many reasons that the Colorado School of Mines piece could be a misrepresentation — including an attempt by someone at the School of Mines to cover up trading away the original Colorado Dragon. But that said, two specimens with the same number, and at least one of those with very questionable historical references? At the very least, one is left with a tremendous sense of uncertainty, and anger that such an important historical artifact is now tarnished. Ed Raines is the Collections Manager at the Colorado School of Mines Geology Museum, and one of the most knowledgeable professionals I know of in terms of Colorado minerals. Ed is also a bulldog – he pursues information with tremendous tenacity, and is a stickler for facts. He understands the importance of Gregory gold, and has scoured the records to shed light on the mystery. Along the way he found a third specimen labeled 5600, now in another private Colorado collection! Two is bad, three is ridiculous.

Another 5600! In a private collection

The picture above shows this third specimen, and its label — identical to the one with the Colorado Dragon. This third specimen was also acquired from Richard Kosnar. Without labels, all three golds would be interesting specimens; with the labels they become locked in the evidence room of speculation and innuendo. Just as labels add to the “value” of many specimens, these simple tags can cast doubt, and ultimately, disgust. The principals in the original transactions may know the real facts, but today there is only conflicting labels and at best, duplicate specimens. In my professional life I am asked to make judgments based on incomplete and conflicting data; I can not conclude anything from this mess other that someone(s) behaved inappropriately.

Why do Collectors Believe?

There are untold numbers of minerals that are inappropriately mated with labels. There are obvious examples where this matching is done with malfeasance – simply mineral fraud. Every collector is also familiar with unintentional mislabeling. This usually occurs when old collections have fallen to a state of disrepair, and labels become disassociated with the physical specimens. There are many tales of collecting apocalypse where carefully nurtured and curated collections that are passed along to uninterested progeny only to end up in a garage sale (I did acquire an outstanding jalpaite thumbnail in estate sale once for the princely sum of 3 dollars!). There are also many labels that are applied to specimens based on “guesses” – some are educated guesses and sometimes they are little more than wishes and hopes (my bideauxite pictured above is now labeled Tiger, but that really is just an educated guess). Unfortunately, once a label is attached to a specimen, however indelicately, it develops some credibility. This credibility resides mostly in the hearts of collectors – it is easy to blame unscrupulous dealers, but in the end it is the collector that decides the value of a specimen. The vast majority of mineral labels are above reproach; if there is something incorrect it is usually based on good intentions (e.g., when I label bideauxite as being from Tiger — no good intention is had by labeling it from Leadville!). However, there are some startling examples where mineral pedigrees that are incredulous, yet are accepted and promoted by knowledgeable collectors. This speaks to the psychology of collectors, especially the most passionate members of the hobby. Their pursuit of minerals can cloud their judgment to point of accepting the flimsiest evidence if it means they acquire something unique.

Barlow Chalcocite: originally sold as Jalpaite

I experienced an example of this power of wishful thinking in the early 1990s when I was asked to write a chapter documenting the silver specimens in John Barlow’s collection. John had acquired an incredible jalpaite, purportedly from the Caribou Mine, located about 20 miles west of the modern city Boulder, from Richard Kosnar. John’s later recollection of the acquisition was that he was skeptical of identification, but when I first saw the specimen in his home in 1993 he presented it as the world’s finest jalpaite – it is pictured above. Peering at the fine miniature, I reacted with typical skepticism and sarcasm – I laughed. I had seen the specimen in the pictured in the Mineralogical Record years before (1976 to be exact), but in person the specimen was stunning….just not jalpaite. Laughing was probably not the best way to start a serious mineral discussion; nevertheless, John eventually had the specimen “tested” at the Smithsonian, and it was confirmed to be a chalcocite. It was a very fine chalcocite, but clearly was not from the Caribou Mine. John eventually came to terms with Kosnar, and decided that it was a chalcocite from Levant Mine in Cornwall, and had come to Colorado as a collectable by William Turnby, a partner in the Caribou mine back in the 19th century. Turnby had spent time in Cornwall, thus, this became “a plausible explanation”. This is how the specimen was labeled in John’s collection when he died. Is the Barlow label believable? Not to me.

The most disquieting aspect of this story is that John Barlow was a very knowledgeable collector – why would he accept this fanciful explanation? John was not duped into his belief by an unscrupulous dealer, but truly believed he had an amazing treasure. This tale is hardly unique – many collectors have labels that they want to believe against a preponderance of evidence.

When Specimens are Historical Artifacts, not Works of Art

Mineral collecting has as many different facets as there are collectors. For many, minerals are works of art; for others, they are expressions of science. For some collectors, including me, minerals collections are ultimately an expression of humanity. Labels tell that human story. When labels go awry – intentionally or accidently, the story of a collection is diminished. Sometimes this is inconsequential, but other times, the mislabeling is historical theft.

The Zen of Stephanite: Collecting Minerals in the Era of Art

The most beautiful experience we can have is the mysterious – the fundamental emotion which stands at the cradle of true art and true science. Albert Einstein

A family gathering of Stephanite – Ag5SbS4 – a black and rather plain silver mineral. From the left, a single crystal from Pribram (crystal is 4.5 cm high, scale for other specimens), a cluster of bright crystals from the Husky Mine, Yukon, Canada, and dozens of prismatic crystals on matrix from Joachimstahl, Bohemia.

I have been collecting minerals for 54 years, and in that half century there has been a dramatic evolution of the “mineral hobby”. Perhaps this evolution is normal, but today the hobby is barely connected to the rock hound roots of my past. I was recently offered an incredible (a more descriptive adjective would be “obscene”) sum for one of my mineral specimens. The dollar amount was more than 3 times the annual salary I drew when I started as an assistant professor at the University of Arizona in 1983. Rather than being pleased with the offer and congratulating myself on the thoughtful investment strategy I must have concocted all those years ago, I was despondent. The collector persisted, and told me the “specimen was a masterpiece, a work of art”. Art! Indeed I collect minerals because they are meaningful artifacts – the perfect combination of science, human history and perfection in nature, but the way the term “art” was being used reduced the specimen to the calculus of trophy hunting.

My depression was an expression of the culmination of frustrations and fascinations with the changes in mineral market I have observed. In the 1960s and early 70s most minerals were within the economic reach of a dedicated mineral collector. There was a “top end” to be sure, and certainly many minerals fetched prices that exceeded the cost of a new automobile. However, there were many collectors that built incredible collections on a bargain budget. These collectors were driven by a passion I can relate to – most were very knowledgeable about mineralogy and had a rudimentary understanding of the geology. In the early 1970s there was a strong push by a group of mineral dealers and curators to describe some minerals as “natural works of art”. Paul Desautels was at the vanguard of this movement, and in 1968 he published The Mineral Kingdom, which is arguably the most influential mineral book in history.

The Mineral Kingdom – a remarkably influential book published by the curator at the Smithsonian in 1968. Although perfection and beauty in mineral specimens had long been sought, The Mineral Kingdom laid out why mineral specimens should be thought of as art.

I received a copy of The Mineral Kingdom for Christmas in 1970. I loved the book (still do) – it has chapters on the science of minerals, the history of minerals, famous localities and countless historical drawings and photographs. It also has chapters entitled “Mineral Masterpieces” and “The Connoisseur”. The opening soliloquy of the chapter on Mineral Masterpieces: “Classic mineral specimens, like great works of art, achieve their status through experts’ judgments”. This sentence is, of course, 100 percent factual – and I would be very hypocritical to suggest that I don’t covet, pursue, and cherish mineral masterpieces. However, this tie to art has driven the mineral market in the last 40 years in ways that are not healthy. In the art world the top end of the market seems to have little relationship to driving prices and value at the low end of the market. That is not true in the mineral collecting world – prices for top pieces provide justification for pricing lesser specimens. The conversation goes like this: I saw a Kongsberg silver wire that was just sold for $300,000 dollars, therefore this lesser Kongsberg must be worth at least $40,000! In the art world no one says that a 25 million dollar Rembrandt sketch of a smiling woman means that similar drawing by Elmer Fudd justifies a price of 1 million dollars.

In my opinion mineral collecting in this era of “minerals as art” has made minerals much less accessible to beginning collectors and those of modest means. The market place is still adjusting, and Darwinian forces will most certainly win out. Luckily, there are still some minerals that have resisted the art trends — mostly very common minerals, very rare minerals, or those that are considered “ugly”. Being a silver collector I am fortunate that some of the silver species fall in later two categories. One of these is stephanite – and as Einstein notes, it is mysterious mineral, at the intersection of science and art.

Minerals as Art

There is a vast body of literature devoted to the psychology and motivations of collectors of high priced art. In truth, art collectors are probably not a lot different that collectors of “any objects” – baseball cards, model trains, stamps, coins, etc. However, there is a special aura associated with art collecting. In November, 2013 Christie’s auctioned the Francis Bacon painting “Three Studies of Lucian Freud” for $142.4 million dollars (there are rumors of private art sales for even more – $250 million for a Cezanne in 2011, for example). To me, the Bacon painting is just flat; it does not move me in any way.

Francis Bacon’s Three Studies of Lucian Freud, painted in 1969. Christie’s sold the painting in auction for more than 142 million dollars, which 7 bidders competing for the right to own….these three panels.

142 million dollars? Those that analyze the art market claim that the value is driven by both passion and competition. The passion is easy to understand, but it is the competition that propels the price sky high. Competition in this case is not the same as demand for a rare resource, although that is a factor. Rather, the competition is about denying others the trophy. This lust for winning strikes a deep nerve. The ultimate trophy is an important aspect in mineral collecting today.

In 2012 the Economist magazine profiled several studies on the art market, including a Barclays Bank report entitled “Profit or Pleasure? Exploring the Motivations Behind Treasure Trends”. The report interviewed 2000 art collectors and dealers (all very rich people) from 17 different countries, and found that this rich clique had a strong sense of community. The collectors, and dealers that cater to them, shared that buying art engendered feelings of victory, cultural superiority and established a badge of social distinction. The sense of community also leads to mechanism of validation – these collectors want what the other collectors want, and were actually quite conservative in branching out on their own, and rarely are trend setters.

Art Basel is an annual art fair in Switzerland that is sort of like the annual Tucson Gem and Mineral Show. Some 300 plus very high end galleries put on a show that is a “do not miss” event for collectors and museums. In the Barclay report there were a number of dealers that talked about their strategies for selling their wares. They often make a list of people they think would be a “good home” for a piece of art, and then show the piece only to those queued on the list. Collectors that have a piece reserved for them personally are nearly twice as likely to buy the art work than if it is openly displayed in a gallery. This last year Art Basel tried an experiment of opening the art show early to select “VIPs”; lesser VIPs had to wait a few hours before they could buy. Predictably, the lesser VIPs were angry – mostly about their demotion in status.

Ikons, a 2007 publication by mineral dealer Wayne Thompson, was a tribute to minerals as art. Thompson makes the argument that visual presence of certain specimens makes them “ikons” — as the art standard for the mineral community.

The description of Art Basel could easily be Tucson if the words “art works” and “mineral specimens” are interchanged. Today the highest end mineral specimens are sold at “pre-show” gatherings at resorts like Westward Look. The well healed arrive a week before the main show in downtown Tucson, and visit the pre-shows. They ask if dealers have anything set aside for them – and the successful dealer always has a stash hidden away, under the bed or in the bathroom, that is just to be viewed by the preferred customer. The “lesser collectors” (people like me – knowledgeable but never a VIP) then can browse the more modest minerals on the shelves of the display cases. I am told that the preferred customers account for 10 percent of the sales in volume and 75 percent of the monetary value.

In 2007 Wayne Thompson published a special volume in the Mineralogical Record. This volume was called Ikons – Classic and Contemporary Masterpieces. It is a homage to minerals as art, and makes the point that iconic specimens are as important at art masterpieces. However, there is a huge disconnect between pricing for mineral masterpieces and lesser specimens. It is always difficult to know what an “ikon” has sold for — rumors help drive up prices — but a simple example illustrates this dilemma.

The Aztec Sun – legrandite — as displayed in the MIM museum in Beirut. This is one of the world’s most famous mineral specimens, and now is a standard for comparison for all legrandite.

One of the most famous mineral specimens in world is the Aztec Sun – a spectacular spray of lemon yellow legrandeite from Mapimi, Mexico. Today the Aztec Sun resides in a fabulous museum, MIM, located in Beirut, Lebanon. This specimen use to be in the Miguel Romero mineral collection, and I had the honor of curating the Romero collection for 5 years. When it was decided to sell the Romero collection this piece was the subject of much angst on pricing. How much was it worth? I don’t know what the actual selling price was, but the rumor was 2 million dollars. It is about 20 cm high, and really, a rather simple mineral; (Zn[AsO4] [OH].H2O). The rumored sales price reverberated through the mineral community, and I know of at least 3 cases where a mineral dealer raised their prices on the legrandite specimens in their stock — in one case the repricing was an escalation by a factor of 3! Why? The specimen that suddenly carried a hefty price tag was hardly the Aztec Sun; in fact, it was a rather unremarkable 4 cm cluster of slightly damaged crystals on brown limonite matrix. A decade later that specimen is still for sale, although now only twice its original price tag.

This dragging up in value of lesser specimens by the sale prices of the “ikons” is a perplexing problem in the mineral hobby. It seems to suggest that a mineral species or its locality is the equivalent to a named artist – i.e., legrandite = Van Gogh. It is difficult to know what the market trend will be for minerals – will they become mineral specimens again, or only works of art?

Stephanite

Stephanite is one of the four “common” silver sulfosalts – the others being polybasite, pyrargyrite, and proustite. Stephanite is known from hundreds of localities, and in the past was a very important ore of silver (in fact, stephanite along with acanthite, was the primary ore at Comstock Lode in Nevada where 200 million ounces of silver were produced). Despite its relative abundance and chemical kinship to the other more highly coveted silver sulfosalts, stephanite is hardly ever considered a “classic”. A picture of stephanite has never graced the cover of Mineralogical Record, and it does not even get a tiny shout-out in Ikons. Stephanite is black, rarely lusterous, and mostly found in small crystals. However, it is a mineral with a rich history, and is an important artifact from every historic silver mining camp in the world. It well may be the antidote to minerals-as-art movement. Stephanite is where I find my Zen.

4.5 cm tall crystal from Pribram, Czech Republic. Jeff Scovil photo.

If there was a “world class” stephanite it would probably be the crystal pictured above from Pribram, Czech. The crystal is of extraordinary size for the species, and a bright luster. The mines of Pribram are quite ancient – silver mining is known here from the 13th century. During the 19th century the Pribram mines were some of the most technologically advanced in the world, and were the first to have shafts that descended 1000 meters below the surface. The best silver species specimens were mostly mined before 1860, and are very well represented in the Narodni Museum in Prague. The pictured stephanite is the best I know of, although it is difficult to document its lineage. Below are the mineral labels still with the specimen; it came to me through Gene Schlepp.

Labels for the Pribram stephanite. Only the last label is recognizable to me - Rukin Jelks (who was a very highly regarded southern Arizona collector).

Labels for the Pribram stephanite. The H. Maucher label most be from the late 1930s. Rukin Jelks (who was a very highly regarded southern Arizona collector) was the last owner before passing the specimen through Western Minerals in Tucson.

The common silver sulfosalts are part of a group of complex chalcogenides with a chemical formula A_xB_yS_n where A = Ag, B = As, Sb or Bi, and the S is sulfur. For stephanite the formula is Ag₅SbS₄. The fact that polybasite, proustite and pyrargyrite are part of the same group means that they all have similar properties structurally – and which of these mineral forms in a geologic environment mostly depends on temperatures and pressures. In almost all cases, the silver sulfosalts form in epithermal veins – hydrothermally driven fluids. Stephanite is the last of these minerals to precipitate out of solution – in fact, stephanite is not stable above 197 degrees C. Above this temperature stephanite decomposes into pyrargyrite and acanthite.

Stephanite on polybasite, Fresnillo, Zacatecas, Mexico. The stephanite is the last silver mineral formed in most epithermal silver veins.

The specimen pictured above documents the paragenesis of stephanite from Fresnillo, Zacatecas, Mexico. The core of the specimen (with is 3.5 cm high) is a polybasite crystal. Sprinkled across the polybasite are stephanite crystals which grew on the polybasite as the vein fluids cooled. Fresnillo is an amazing silver deposit, and source of some of the very best silver sulfosalt specimens in existence. Mining at Fresnillo dates from Spanish Colonial time, although few specimens survived before the mid 1970’s. Fresnillo is often mentioned as an important silver district in historical literature, but it really was quite unremarkable. The district was nearly abandoned in the 1970’s, but a desperation drilling program discovered a blind vein system a couple of kilometers southeast of the main workings. These veins average 800 g/ton of silver, and occasionally grade to 2000 g/ton. Seams of solid pyrargyrite 35 cm thick have been reported and individual crystals more than 10 cm in length have been collected. The district has now produced more than a billion ounces of silver (Kongsberg only produced 43 million ounces of silver!), and exploration in the surrounding region has located huge reserves. Many of the best specimens came out in the period of time 1992-1999; I was extremely fortunate to have seen most of the best material, and acquired the core of my collection from Dave Bunk during this time.

Stephanite was first mentioned in literature in 1546 by Georgius Agricola. Agricola, born Georg Bauer, is the “father of mineralogy”; he was the town physician at the Bohemian mining center of Joachimsthal, and wrote extensively on the geology of the region. In his 1546 text De Natura Fossilium Agricola described the mineral as schwarzerz in reference to its black color. It is later referred to with various names – both in latin and german – as black silver ore and brittle silver ore. In 1845 Wilhelm Haidinger proposed the modern name of stephanite in honor of the Archduke of Austria, Stephan Franz Victor. Archduke Stephan was one of many nobelmen of the time that built “natural history cabinets” — however his was just extraordinary! He acquired more than 20,000 specimens, mainly from the mines of Bohemia. When he died the collection went to the House of Oldenburg. Much of it was sold, but some of the specimens remain in the Natural History Museum in Berlin. The Archduke’s labels are distinctive, and much coveted by mineral collectors today.

A complex cluster of stephanite crystals from Freiberg, Saxony. The specimen is a little over 5 cm tall. The specimen was originally in the Archduke Stephan collection, and has passed through at least 5 collections before coming to me.

Stephanite belongs to orthorhombic crystal class, although twining on the prism planes is extremely common giving rise to pseudo hexagonal crystals. There are three dominate habits for stephanite: (1) thin, hexagonal plates that can be as large as the size of a US quarter, (2) elgonated hexagonal prisms (like the Pribram stephanite pictured above), and (3) tubular clusters of crystals that form branching clusters. Stephanite is iron-black in color and sometimes has a bright luster. There are numerous mineralogical texts that claim the bright luster will dull with exposure to sun light, but I have no evidence of that, nor do I know what the physical mechanism would be.

Stephanite prism, Fresnillo, Zacatecas, Mexico. A classic pseudo hexagonal prism, 2.7 cm tall. Some of the very best stephanotis ever recovered came from Fresnillo in the late 1990s. Jesse La Plante photography.

The largest stephanite known are from a modest mine, the Las Chispas, located near Arizpe, Sonora, Mexico. The production history of the Las Chispas is mixed; it was interrupted by revolution, strikes and seizure. The total silver produced probably did not exceed 20 million ounces of silver, but a very enlightened mine manger, Edward Dufourcq collected specimens and the mine owner, Pedrazzini, donated many to the Columbia School of Mines. Dufourcq wrote the following in an article published in 1910; “The crystallized specimens of the silver minerals are especially noteworthy….What is probably the largest single specimen of stephanite in the world was presented by Mr. Peddrazzini to the Egleston collection at the Columbia School of mines, where there are also a number of other specimens of polybasite and stephanite, as well as a remarkable specimen representing the transition of an argentite crystal into cerargyrite and a fine embolite. The American Museum of National Hisotry in New York also has, from this mine (the Las Chispas), what is probably the largest mass of polybasite crystals ever taken out in one piece. This originally weighed over 65 lb., but was broken into two parts during the time it was in transit from Sonora to New York”. When I was curator at the University of Arizona Mineral Museum we received one of the two pieces of the “65 pound” polybasite crystal group in trade – it only weighed 13 pounds! The stephanite groups are smaller than the polybasites, but still giants for the species. The largest I know of is a cluster of crystals 12 cm across. The photo below is a very large crystal group in my collection.

Stephanite, Arizpe, Sonora, Mexico. A large cluster of crystals from the Las Chispas mine; the specimen as displayed is 6.8 cm across. Jesse La Plante photograph.

Stephanite has always been a favorite of serious collectors, even if it is not in “art world”. Below is the mineral advertisement from the Foote Mineral Company of Philadelphia. Albert Edward Foote, who arguably is the most famous mineral dealer in American history, sold minerals from 1875 until his death in 1895 (the company passed to his son, a good dealer in his own right, and then to others and still exists today). The ad below includes a reference to “Stephanite, fine crystals, 75 cts to $5″ from Germany.

Mineral advertisement from A.E. Foote Minerals published in 1894. The stephanite specimen pictured below was one that was sold with this ad, and costs $3 dollars 120 years ago.

I bought a stephanite in 1988 (pictured below) that came with a photocopy of this ad, and a note that the specimen was purchased from the ad for $3 dollars in 1894. It is impossible to confirm that this is indeed true, but it does provide a fanciful barometer for price increases. I bought the specimen for 450 dollars – which translates into an escalation of a factor of 150. There are many “inflation calculators” that can help give a sense of the rising costs overall. These calculators say that consumer goods have increased by a factor of 20 over in the last 100 years (averages 3% a year), thus stephanite has been a “good” investment. But the 3% annual inflation is highly misleading – some commodities have increased in value and others have dropped tremendously (for example, the cost of electricity). Another way to compare the value of the price increase is to compare it to a specific commodity through time. For a mineral collector the perfect barometer is the cost of a pint of beer (mineral collectors, in general, think in terms of specimens and beer). Using the average price for a pint of beer in a bar in New York City in 1900, and again in 2000, the cost increase was a factor of 180 (data from the Economist). In other words, stephanite prices have not kept up with the price of beer. This truly means that stephanite is not art!

Stephanite, Frieberg, Saxony, Germany. A large thumbnail, originally bought from the A.E. Foote mineral company in 1894. Jesse La Plante photograph.

Mineral Collecting in the Era of Art

There are a number of ways to evaluate the value of a mineral specimen. These include rarity, locality, pedigree, and aesthetic beauty. Beyond the specific character of an individual specimen, it can have value as part of a collection, documenting the nature of a particular mine or geological deposit. Unfortunately, the evaluation criteria are highly subjective and subject to changes in mineral availability and popular notions of aesthetic beauty. In the last 20-30 years the “masterpiece” or trophy mineral has dominated the pricing paradigm in the hobby, and dramatically skewed the sense of worth. Wendell Wilson and John White (1977) conducted an experiment in specimen appraisal by asking a group of museum curators, collectors, and mineral dealers to estimate the cost of ten different mineral specimens. The survey was conducted twice, four years apart. Although the time separation was too short to gauge slowly varying trends (like specimen size), it did capture the strong trends in trophy hunting. During this four-year period the average mineral specimen increased in value by 190%! Although not immediately obvious, this dramatic increase caused a cosmic shift in mineral dealing. Dealers began to view specimens as an investment and certain new collectors demanded a high rate of return. Those dealers that understood the trend were able to adapt the business practices of the art market. However, this adaptation had some very unexpected consequences – all mineral prices became pegged to the highest priced trophies. This meant that “esthetic” but otherwise unremarkable mineral specimens rose in marketing value at an unprecedented rate. By the early part of the 2000s large numbers of collectors had either stopped buying, or were now buying specimens with much less frequency. Today, the mineral collecting hobby is changed – and will continue to change — and is no longer the bastion of “rock hounds”. The question I am most frequently asked today is “how much is that worth”. Almost never am I asked about why a specimen is important, or why I enjoy it.

Fortunately, I can still enjoy my hobby through scholarship, and the pursuit of a few, largely unappreciated species. The Zen of Stephanite.

2.8 cm prism of stephanite with white calcite crystals, from Fresnillo, Zacatecas, Mexico.

A rolling stone does gather moss; return of a silver specimen and the meaning of collecting

Truth is the property of no individual but is the treasure of all men. Ralph Waldo Emerson

A label from the collection of Archduke Stephan, dating in the mid 1800s

I often get asked why I collect minerals, and in general I ignore the inquiry because the answer is a thesis not a sentence. Recently I had returned to me several silver specimens from my collection that “disappeared” for 2 years. The conditions of the “disappearance” is a tale of poor decisions (mine), disorganization (a middle man) and opportunistic dishonesty (a mineral dealer of questionable ethics). However, fate and friends dealt a favorable hand and the specimens were returned (although one was damaged), and my joy in return of the prodigal stones gave me a chance to explain my rationale for collecting.

Frieberg silver wire, 6 cm high. I acquired this specimen in 2010, and it was first cataloged in a collection in 1832.

The centerpiece of the missing specimens was a silver wire from the great German locality of Freiberg. The specimen is a little over 6 cm high and has a patina of age giving it a glow of significance. The specimen was first documented to be in a collection in 1832, and it passed through at least 9 different owners before it came to me. The specimen has beauty to me, but more importantly, it is an artifact of history and humanity. This particular specimen has aesthetics, and its form is an interesting mineralogical tale. In addition it is from a mining locality that has a rich history, and once the silver wire was mined, it was a prized natural history specimen that was passed along to collectors that had the same passion as I.

Collectors: Evolution or Illness

There are dedicated collectors in every society, and these collectors are not defined by economic or social class. There is a large body of literature on the psychology of collecting (most of which I find pompous and over reaching!), and there are two basic schools of thought. The first is the Freudian view that says collectors are afflicted with a compulsive disorder; collecting is emotional and a desire to control or connect. The second view is the collecting is an evolutionary trait associated with amassing treasure as a survival instinct. Neither of these synopses really describes the passion that most serious mineral collectors I knew feel.

The vast majority of mineral collectors I associate with feel joy in finding a natural object that has beauty and form. There are mineral collectors that pursue specimens as investment or status. However, they are usually of the “moneyed class”, and they represent something different that most of the collectors I know, although the first prominent mineral collectors were indeed from the rich and powerful. Mineral collecting began in the 18^th century by aristocrats – they assembled cabinets of rocks and minerals, and these cabinets were badges of social class. Perhaps the most famous of these early aristocratic collectors was Archduke Stephan Franz Victor von Habsburg-Lothringen. Born into the Hapsburg Royal Court, Stephan was well educated, and destined to a life not sullied by common labors. He built a mineral collection and cabinet that eventually contained more than 20,000 specimens. The top figure in this posting is one of Stephan’s labels – there are many mineral collectors that value a Stephan label almost as much as a mineral. The stephanite specimen below is also from Freiberg, and was once in the Archduke’s collection. Stephanite is named for Stephan.

Frieberg stephanite, 7 cm high, acquired in 2008. This is an extraordinary stephanite crystal group, and has spent part of its “life” in two museums and three private collections before coming to my collection.

Collecting Silver

I first started collecting minerals at age 4 or 5, fostered by the passion of my father who loved collecting minerals in the field. At least a couple of times a month we would journey to mines or mineral localities in New Mexico, Colorado or Arizona. I can’t really say why my father was such a dedicated field collector – he was a chemist by profession, but the science of minerals did not seem to be what was important to him. He was raised in the home of his grandfather who was a prospector in Arizona, and this man seemed certain that the next great lode was hidden in the deserts and rugged mountains of Arizona just waiting to be discovered. This lust of treasure hunting more describes my father’s passion – he was not really looking for the mother lode, but he loved finding a great specimen in the ground. Once we got the rocks home he was far less interested in them – the pursuit was his passion. He built an extraordinary library for topographical mineralogy – boxes and filing cabinets filled with Xeroxed reports and papers from obscure journals. He assembled this material to map out where to go and collect next.

My brothers and sisters often accompanied my father on our journeys through the southwest. However, none of them became mineral collectors, nor even really dabbled in collecting. Clearly, mineral collecting is not a simple matter of nurture. My first mineral collections were mostly driven by form – I loved euhedral crystals with sharp faces. By age 10 I had a catalog for my collection that numbered in the several hundred; within a few years after that I was actively trading many of my specimens with a dealer in Albuquerque in an attempt to acquire “better” material. In high school I had my first serious cull of my collection after which I would only collect sulfide ore minerals. I had a very fine collection of galena, pyrite, chalcopyrite and a few chalcocites!

Freiberg acanthite, 5.5 cm high. This specimen was acquired in 2002, and has been pictured in numerous publications

I continued to refine my collecting until the early 1980s when I decided to only collected silver minerals. Although I am interested in nearly all minerals, my focus is quite narrow. There about 4600 different mineral species known, and approximately 160 of them have silver as an essential element; of these, only about 15 are “common” or available as crystals that are easily seen with the naked eye. Silver has been reported from more than 20,000 localities world wide – approximately 100 different localities have produced quantities of very well crystallized specimens of the common silver species. In my collection today I have samples of 109 of the different silver species, and I have every important locality represented.

Freiberg

The wire silver from Freiberg is a quintessential specimen from my collection. The Erzgebirge are a modest mountain range that runs along the boundary between southeastern Germany and the northern part of the Czech Republic) for about 100 km. The English translation of Erzgebirge is “Ore Mountains”, and these rolling hills are the birth place of modern mining, metallurgy and mineralogy. The German side of the Erzgebirge is known as the Saxony side, while the Czech side is referred to as Bohemia. The Bohemia mines of fame include Kutna Hora and Jachymos/St. Joachimsthal, while the Saxon mining areas of note are Schneeberg and Schlema, Annaberg, Marienberg, Johanngeorgenstadt, and the most famous of all, Freiberg.

The story of the Erzgebirge silver is voluminous topic; a simple summary of Freiberg serves to at least stake the claim of the Ore Mountains as being the most important silver mining camps in history. Silver was first discovered in Freiberg in 1163 – the area is located about 30 km west-southwest of Desden. The town was officially founded in 1186, and over 800 years of mining produced about 8 kilotonnes of silver. The two most famous Freiberg mines are the Himmelfahrt and Himmelsfurst – these were large mines with multiple shafts. The enduring influence of Frieberg came with the founding of the Bergakademie Frieberg, or Frieberg Mining Academy, by Prince Franz Xaver in 1765. The mining academy in Freiberg can now lay claim to the oldest School of Mines, and can lay claim to educating some of the most famous mining engineers and mineralogist in the world. A.G. Werner, a mining geologist on the faculty first proposed a chemical classification of minerals in 1774 – he invented the modern scheme for describing minerals. The Frieberg Academy had a profound effect on mineralogy also be preserving specimens that came from the mines and build a remarkable mineral collection.

Freiberg silver, 7 cm high, acquired in 2001. This is a classic example of wire silver that must have grown from the decomposition of acanthite. The wires have been exposed by removing the encasing calcite.

I had the chance to visit the Freiberg Academy in the summer of 1991. The Berlin wall had just fallen, and East and West Germany had reunified. It was clear as I drove from Frankfurt to Dresden that there really were two Germanys. The infrastructure in the east was third world, and as I drove through Dresden there still were Soviet tanks deployed. However, when I got to Freiberg, the Academy staff were incredibly warm and helpful. What I saw in the collections was amazing, and made my connection to my Freiberg silver minerals much richer.

Freiberg Pyrargyrite, field of view is 1.7 cm. This specimen was acquired in 1984, a came through a dealer that had traded it out of the American Museum of Natural History in New York. The AMNH is one of the great mineral museums in the world, and received the collections from the Columbia School of Mines in the early part of the 20th Century.

Silver has an affinity for anions of sulfur, selenium and tellurium, all of which have similar ionic radii. These minerals are known as the silver sulfides (in the nomenclature of Dana, these include the tellurides and selenides), of which the acanthite group is the most common. The acanthite group includes the simplest sulfides (the most common of these are acanthite, argentite, aguilarite, naumannite, hessite, petzite, empressite, jalpaite, stromeyerite and eucairite). This group of minerals displays the characteristic of temperature-dependent dimorphism. At high temperatures these minerals are usually cubic or hexagonal, whereas at lower temperatures the minerals display an orthorhombic or monoclinic crystal structure. The transition temperature is usually between 130 and 180^o C. Acanthite and argentite are the most common dimorphic pair. Acanthtite is the form that is stable at room temperature, so even when a specimen appears to have cubic crystals, it is a monoclinic microstructure frozen in the cubic frame. The same thing that makes the silver-sulfur bond temperature dependent also makes acanthite sensitive to decomposition when temperature and pressure change – silver is released from the sulfur bond and grows wires out of the acanthite. Silver wires are extremely common, and it is clear that they are all formed by the decomposition of a silver sulfide (most likely acanthite). This was first observed and understood at Freiberg.

An early explanation for the growth of silver wires by the decomposition of acanthite

The rest of the story of the mineral mystery

I have wanted to write a book on the silver minerals for a long time. Gloria Staebler has provided me the encouragement to pursue this book which will be years in the making. Along the way I decided to illustrate certain aspects of the mineralogy with pictures of many of my specimens. Photographing minerals specimens is not easy under the best of circumstances, and silver minerals are extremely difficult. Their dark color, intergrown crystals, and occasional high luster means that most attempts to capture their beauty with a camera result in images that closely resemble black ink blots. With this in mind, I sent a subcollection of the specimens to be photographed by one of the best mineral artists in the world. However, sending multiple specimens to be photographed far from my immediate control was a poor decision. It took several attempts to get the images right; over time one small box of the specimens are returned to the wrong owner. Although I did not get back my specimens there was no documentation that I did not get back these back – in fact, many people assumed I simply had misplaced them. I knew that was not the case, but I was frustrated in locating the silvers.

Advertisement in the Mineralogical Record that featured my Freiberg silver. Read the ad – this is what is wrong with mineral collecting today.

In late February of this year I received the March-April issue of Mineralogical Record. As usual, I first read the most interesting article to me, and then thumbed through the rest of the volume looking at advertisements from various mineral dealers. As I turned the pages I was stunned – there was a picture of my Freiberg silver in the ad of dealer for sale. I was outraged! Indeed my specimens had been returned to the wrong owner, but that dealer chose to assume that mistake was fortuitous! Found wealth! The repatriation was emotional and messy, but I am reminded again that honesty is a rarer commodity than it should be. The fortuitous dealer claims that he did nothing wrong at all – in fact, he simply just thought the minerals were his, and he had forgotten how he got them.

This story is not done, but in most ways the universe is again right. However, the story of a mineral lost is also a tale about collectors and the mineral hobby. When I first started in the hobby more than 50 years ago it was different. There were far more scholars than today. My sense is that this is not because there is less interest in mineralogy, but because the opportunities to build a meaningful collection are greatly diminished. Prices have escalated – this is always true in collectables – but in a very dramatic way collecting is out of reach for the person of average means. I have benefited occasionally from this “art pricing model”; specimens I bought for hundreds of dollars I have traded or sold for 100 times purchase value. New collectors do not have the “hundreds of dollars” specimens available to trade or sell to better create a collection, and thus, they tend to drift away. The case of the dealer wanting to sell my “fortuitously” purloined silvers is symptomatic of the commercial side of the collecting equation. Not something to be happy about, nor do I see an enlightening horizon.

Stories in Stone: Mineral Collecting and the Tucson Gem and Mineral Show

A rock or stone is not a subject that, of itself, may interest a philosopher to study; but, when he comes to see the necessity of those hard bodies, in the constitution of this earth, or for the permanency of the land on which we dwell, and when he finds that there are means wisely provided for the renovation of this necessary decaying part, as well as that of every other, he then, with pleasure, contemplates this manifestation of design, and thus connects the mineral system of this earth with that by which the heavenly bodies are made to move perpetually in their orbits. James Hutton, the Father of Geology, 1795

Moon Rise over the Catalina Mountains — Start of the Tucson Show, 2014 (photo, Michelle Hall)

One of my very first memories — vivid in my mind but probably a mixture of early experiences – is collecting topaz crystals with my father in west-central Utah. Today, I know we were at Topaz Mountain, but my childhood memory is an image of a sandy wash on a cold winter day. I was probably 4 years old given that my father was on temporary duty away from Los Alamos and working at the Dugway Proving Grounds. My father had made a couple of screens, and we were shoveling the sands of the wash on to the screens and sorting through the leavings for nearly colorless topaz crystals. We found then by the bucket load, and I remember holding in my hand dozens of crystals that sparkled brightly in the sunlight. I don’t really remember what I was thinking when I held those crystals, but I have been collecting minerals ever since that trip. In the 54 years or so since that memory I have searched through a thousand mines in the western US for minerals, built a dozen collections, made large rock gardens, sold thousands of minerals to buy a few hundred, and visited every mineral museum I could find in the world. I discovered mineral shows in the 1960s, and in 1973 my father and I went to our first Tucson Gem and Mineral Show. It was an amazing experience for me – we first went to the Desert Inn, and I could not believe the array of minerals for sale on the top of beds in a hotel! However, it was the main show that hooked me forever. On the show floor were special exhibit cases, and one of the very first we visited was Harvard case, which contained what I think, is the world’s most famous mineral: a 5-inch tall “ram’s horn” of gold from Colorado. I was spell bound! And right next to the gold was cerussite from New Mexico that was so much better than anything I had ever seen from my home state that I was in disbelief. I have not missed a Tucson show since that time!

The experience of that first Tucson Show had a profound effect on me, and it is fair to say it shaped my life. I went to New Mexico Tech for my undergraduate degrees, and many weekends were spent collecting minerals from all over New Mexico – these were the seed corn to my personal collection. Every February I would load up my pickup with the spoils of my efforts and head for Tucson. I would sell everything (for a lot less than I hoped) to a couple of dealers in motel rooms, and then use the money to buy 5 to 10 minerals for my collection. Nothing was easy, but 1970s were a far different time, and there were many mineral dealers interested in good, colorful low-end specimens in bulk. I still have 3 specimens that I purchased in those heady days. When I graduated from Caltech in 1983 with a degree in seismology I had 4 different job offers, but there was only one that I wanted – a professorship at the University of Arizona. I am a bit embarrassed to say that I based my career choice not on scholarly reputation, but rather on the opportunity to live at the center of the mineral collecting universe!

Catalogue number 1 in my present collection – a wire of silver from Kongsberg purchased at the Tucson show in 1978

The 2014 Show

2014 is the 60^th Anniversary of the Tucson Gem and Mineral Show. Every year they have a theme, and this year in honor of the 60years of bringing thousands of collectors from around the world to southern Arizona, the theme is “Diamonds, Gold and Silver”. The theme serves as a focus for special exhibits on the show floor, and I committed to put in several cases of my minerals and help organize a community display (in general, I do not like to display my collection – in fact, I don’t particularly like to show my minerals even in my own home).

Since the mid-1980s I have exclusively collected silver and silver minerals. Although I enjoy mineralogy and mining in general, silver is my passion. Else where I have written about silver: “For many collectors, the word conjures up images of baroque ropes of white, lustrous metal from Kongsberg or beautiful herringbone plates from Batopilas. For other collectors, the vermillion red of a Chanarcillo proustite is the most alluring color of all specimens. Silver and silver-bearing minerals are part of the nobility of the mineral kingdom; no other group of minerals has more associated mining lore or history. Silver financed empires and great wars. Silver is said to have magical purifying properties, and alchemists promised secret processes to turn lead into silver (both of these myths are partially true!). To the mineral collector, silver minerals hold a particular fascination. Superb specimens are known from hundreds of localities worldwide, and unlike gold, silver is quite a reactive element, forming more 160 different silver-bearing elements”.

I brought minerals for two cases: one focused on native silver and acanthit group minerals (acanthite has the formula of Ag2S, and the acanthite group minerals include some substitution for silver like Japlaite and Sylvanite, and there are also substitutions for sulfur including tellurium and selenium for Hessite and Naumannite ), and the other focused on pyrargyrite, proustite, stephanite, polybasite, and handful of other silver minerals that were some of the best of their kind.

In front of my two cases – (1) silver and acanthite minerals, and (2) common silver sulfosalts

The Silver and Acanthite Case

Silver owes is wonderful qualities to its placement on the periodic table. Silver has an atomic number of 47, and sits below copper and above gold. These two metals are in many ways similar to silver, but they show relatively more and less mineralogical diversity. Gold is heavier and a larger atom, from which it is more difficult to remove electrons. Thus, gold tends to stay mainly in the native state or form semimetallic compounds with tellurium and silver. A copper atom, on the other hand, is smaller than an atom of silver and can readily give up either one or two electrons in the process of forming compounds. This allows for the formation of many more copper minerals than silver minerals including copper silicates and carbonates. All three metals have similar atomic structures, which is a face-centered cube held together by metallic bonds. A characteristic of a face-centered cubic lattice is that the metals are extremely malleable and ductile as well has good conductors of heat and electricity. Silver has the highest conductivity of the metals. Native silver has a bright white color; it has the highest reflectivity of any metal in the visible spectrum, and thus appears to “shine”.

Silver is relatively abundant but dispersed in the Earth’s curst. Magmatic activity concentrates silver, and the vast majority of silver deposits are related to volcanic activity

When not in its native form, silver is generally monovalent (Ag⁺¹). The silver atom has an affinity for anions of sulfur, selenium and tellurium, all of which have similar anionic radii. These silver minerals are known are silver sulfides (in the nomenclature of Dana, these include the tellurides and selenides), and are the most important ore minerals for silver. The acanthite group is the most common and simplest of the sulfides. This group includes acanthite, argentite, aguilarite, naumannite, hessite, petzite, empressite, jalpaite, stromeyerite and eucairite. This group of minerals displays a remarkable structural phenomena called temperature-dependent dimorphism. At high temperatures these minerals are usually cubic or hexagonal, but at lower temperatures these minerals exhibit orthorhomibic or monoclinic structure. The transition temperature is usually between 130^o and 180^o C. Acanthite and argentite are the most common dimorphic pair, and most specimens of acanthite seen in mineral collections show a cubic or octahedral habit “frozen” in at the higher temperature of formation.

Silver Sulfosalt case

The “common” silver sulfosalts Case– proustite, pyrargyrite, stephanite and polybasite

Silver sulfosalts are the most beautiful group of silver minerals. The sulfosalts are composed of silver, lead, and copper as cations and at least one semimetals (arsenic, antimony, or bismuth) linked with sulfur in anionic groups. Two of these sulfosalts are proustite and pyrargyrite are known as the “ruby silvers” because of their translucent red color. In the ruby silvers the anionic group is either AsS₃ (proustite) or SbS₃ (pyrargyrite), arranged in a trigonal pyramid. The semimetal is at the apices of the pyramid, with the sulfur atoms at the base. Silver atoms connect the group in such a way that each sulfur atom has two nearest silver atoms. Both proustite and pyragyrite are light sensitive; exposure to certain wavelengths of light break one of the sulfur bonds and liberate a silver atom that migrates to the surface of the crystal face. Over time ruby silvers become black, which is the result of a thin silver coating on the crystals that quickly reduces to acanthite.

Although there are more than 160 silver bearing minerals, only about a half dozen are relatively common in macroscopic crystals. The simplest of the silver minerals belong to a group called the silver halides, which are ionic bonds between silver and C, Br, or I. The largest number of silver minerals are sulfosalts (including proustite and pyrargyrite) with more than thirty distinct species. The two most common in crystallized specimens are stephanite (Ag₅SbS₄) and polybasite (Ag₁₆Sb₂S₁₁).

A family of prostate crystals from the sulfosalt case — very hard to get the red right, but great crystals one and all.

The Kongsberg Case

I also organized a community case on Kongsberg, which is the most famous locality for native silver in history. When silver was chosen as a theme for the show I knew we had to put together a case on Kongsberg. I volunteered to get a couple of the famous collectors to commit to bringing a few specimens to be put in an exhibit. The fraternity of silver collectors is relatively small, and we all know each other. It was easy to get people to commit — but it was harder to get the contributors to limit the number of specimens that they brought!

Highlights of the Show

The MAIN Tucson Gem and Mineral Show is always an event. The show lasts 4 days, and the Tucson Convention Center and Arena is filled with mineral, gem, fossil and jewelry dealers along with spectacular special exhibits and seminars and talks. The public paid attendance is about 35,000, but the actual attendance with dealers, exhibiters, students and guests is probably about 50-55,000 people. Anyone that is a serious mineral collector comes to this show, and it is very international. It is fair to say that most of my closest friends are in this community, and the common interest of things “mineral” creates a strong social fabric.

The opening of the show on Thursday is a mad rush – and mostly serious mineral people. Within an hour the floor is swarming with people looking through dealers stock, and after that, cruising the special exhibits looking at the treasures that come from around the world. My experience is that not too many minerals are sold on Thursday, but lots of decisions are made. Those decisions are consummated on Friday and Saturday (and for the most part, the mineral community believes that all sales are negotiations, so serious work is needed before minerals exchange hands).

11 am opening day at the Tucson Show, one hour after the doors opened. This is the booth of my friends Dave Bunk (Dave Bunk Minerals) and Gloria Staebler (Lithographie).

Every year the most asked question is “what’s new for this year”, meaning what new mineral discovery has happened in the last year and is marketed in Tucson. This year the biggest news are some extraordinary azurite crystals from Milpillas. Milpillas is a copper mine in Sonora, Mexico, across the border from Bisbee, Arizona. Milpillas mining operations entered a zone of carbonate rocks in 2006, and wonderful copper carbonates flooded the market. The quality was on par with the best ever – similar to Bisshee from the turn of the 19th/20th century and Tsumeb in the mid-20th century. About 2 years ago the oxide zone was exhausted, and it seemed that the Milpillas era had come to an end. The mining begin in the sulfide zone and the milling operations were altered to reflect the sulfide feed stock. However, six months ago the mining encountered a fault zone that had allowed the carbonate mineralization to occupy a sliver within the sulfide zone. It seems that mining management turned a temporary blind eye to the miners collecting the fault zone since the milling process was already adjusted to a different chemistry, and some truly extraordinary azurites have come to light. In my opinion these may be the finest azurites in history; however, thee are thousands of pieces for sell, so there is a psychological numbness to importance of this mineral find. Ten years from now the entire mineral community will talk about the “great old days” for azurite crystals.

Milpillas azurite in Evan Jones’ booth at the Tucson Gem and Mineral Show.

My favorite part of the show is the special exhibits. It is like visiting museums and great private collections from across the world. There were great displays on the theme – diamonds, gold and silver. One of the many surprises was the Smithsonian display on diamonds. They literally had a pile of diamonds that had been confiscated from smugglers that get turned over to the museum.

Pile of diamond — the Smithsonian Institution.

There are more than 130 exhibits, and the vast majority are wonderful. A couple of the exhibits were very unusual though and caught my eye. For 4000 years mankind has been carving gemstones and minerals for decorations. We have a fascination with the natural beauty of stones and the perfection of nature to present color and form. One of the cases that I really liked this year had polished slabs of rhodochrosite and malachite – pink and green. These slices were cut from stalagmites, and the concentric rings are not unlike the growth rings in a tree. The display matched the size for these stalagmites to make for a stunning display.

Slices of rhodochrosite and malachite.

The University of Arizona Mineral Museum had several displays, all very good. However, one had special meaning to me — gold, silver and platinum from the Hubert C. de Monmonier collection. This was the last major donation I worked on as curator of the Museum, and is a fabulous, eclectic collection built over a life time. Hubert was a man of modest means but he built a world case collection; 871 mineral specimens including 350 quartz specimens, 146 tourmaline, 44 silver, 38 beryl and more than 70 gold specimens.

Gold and platinum from the University of Arizona Mineral Museum.

Another favorite case for me was assembled by Dave Bunk to show the best of Colorado silver. There are three mining districts in the state that stand out: Aspen, Creede and Leadville. The two former districts have produced the bulk of notable specimens. Dave collected specimens from private collections (his own, Bryan Lees and Ed Raines in particular) as well as the museums at the Colorado School of Mines and the Denver Museum of Natural History.

Included in the case were some historic artifacts — a vase made from Aspen silver, and a chunk of the largest silver “nugget” found at Aspen (it is the block in the upper right hand corner of the picture of the case).

Smuggler Mine silver “nugget” found in 1894 weighing 1840 lbs. The Dave Bunk display contained a piece that weighed about 5 pounds!

Finally, a case that I really enjoyed celebrated birth of modern crystallography under one of the founders of mineralogy, Abraham Gottlob Werner. Werner was born into a mining family, and he studied mining (and law) at Freiberg, which is an grand locality for silver and silver minerals. In 1775 he was appointed an instructor at the Freiberg Mining Academy, and he published the first modern textbook on descriptive mineralogy, Von den äusserlichen Kennzeichen der Fossilien. The case displayed a collection of wood crystal models that were hand made to illustrate the various classes and forms.

The wood crystal models created at the direction of the father of modern mineralogy.

The Tucson Show is always an experience – educational, social, and even spiritual. This year’s show is special for its exhibits. Although the sense of wonder that I had when I first went to the show in 1973 can’t be duplicated, the show still is grand on an international scale. Tucson itself is fabulous in its own way with a unique flora and fauna, and skies that are magic in the winter. Still much show to go in 2014, but it has already been a great event.

Close of the 2014 Tucson Gem and Mineral Show. Sunset behind Wasson Peak

History Locked in Stone: Why Hessite is a Noble Mineral

Every block of stone has a statue inside it and it is the task of the sculptor to discover it — Michelangelo

One of my favorite places to visit is the Naturhistorisches Museum Wien (Natural History Museum of Vienna). As far as natural history museums go, it has to be the most important in the world. It has display space of 8,500 sq meters (about 94,000 sq ft), and it is filled with more than 30 million objects. The exhibits are decidedly old school: instead of modern interactive computer screens meant to entertain, there are taxidermy marvels documenting the discoveries of the great 18^th and 19^th century naturalists that explored the world as scientists. There are great fossil finds, meteorites, and stone-age works of art, and of course, there is a fantastic collection of minerals!

The museum was built to house the collections of the Habsburg Empire. The House of Habsburg ruled much of eastern Europe between the late 16^th century and World War I. Emperor Franz Joseph I is credited with creating the museum in the mid-19^th century, and the present building opened its doors in 1891. The core of the mineral collection is from the great mining regions that the Habsburgs controlled—Bohemia, Hungary, Austria, and what would become Romania. The oldest specimens were acquired by Archduke Ferdinand II, assembled in what is known as the “Ambrasian Collection”, and brought to Vienna in 1806.

To me, the minerals from the great Eastern European mining centers are masterpieces. Not only are they fine aesthetic specimens, but they are also artifacts that capture human history. Just as Michelangelo spoke of “releasing” the great artwork contained within a block of marble, the minerals that were collected out of the mines of Pribram, the Harz Mountains, Freiberg and Tyrol contain the stories of empires, miners, the birth of mineralogy, and the passion of collectors. Life was hard in the mines, backbreaking, dangerous work with a single goal—to produce bullion.

In Europe the rise of interest in natural sciences meant that unique specimens were preserved starting in the late 18^th century. These specimens went to the collector cabinets of scientists and wealthy gentlemen. The specimens were studied and catalogued; eventually they made their way to museums or other collectors who added their labels and love, until today we have lumps of silver or gold ore that tell a human story. The tradition of collecting minerals from the mines was not passed to America until the latter part of the 19^th century. The mines on the Comstock Lode on the eastern slope of the Sierra Nevada were some of the biggest silver producers ever; but they were discovered in 1859 and exhausted in about 20 years, so the number of documented specimens from the Lode is remarkably few. It is hard to imagine what mineral collections would look like today if the Comstock had been located in Bohemia.

My favorite mineral in the museum is a spectacular cluster of hessite crystals, with associated quartz crystals. The specimen vaguely looks like a hand with the two fingers extended. The overall length is about 10 cm. Hessite is a silver telluride (Ag2Te) and usually is a dull gray. Hessite forms in medium or low temperature hydrothermal veins and is fairly widespread but almost never as crystals or even recognizable masses. What makes the Vienna piece so amazing is that the crystals dwarf most others in the world. The specimen is from Botes, Romania. There is a relatively small series of mines in the “Golden Quadrilateral” in Transylvania that for a few short decades produced a quantity of hessite that is unequalled in quality. In fact, Botes hessite is so outstanding compared to other localities that it is often considered a “single locality” mineral.

The northwestern quadrant of Romania is known as Transylvania, a high plateau surrounded by mountains. Upon hearing the name “Transylvania” the average person has visions of vampires and Dracula; however, to a serious mineral collector the name evokes visions of spectacular gold specimens, rare gold tellurides, and absolutely amazing hessites like the one in the Vienna Museum of Natural History. The “Golden Quadrilateral” is a region shown in the figure below that defines the largest gold resource in all of Europe. More than half of the gold ever mined in Europe came from within the 500 sq km of the Quadrilateral, and it remains the continent’s largest gold reserve. Along a north-northwest trend near the ancient town of Zlatna are a series of amazing deposits in the Apuseni Mountains. These deposits are calc-alkaline volcanic centers that are the response to the collision of Italy to Europe. The volcanoes were active between 15 and 2 million years ago. The map below shows these centers in orange, one of these is marked with a “B” which denotes a modest mountain known as Botes Hill.

Mining for gold in the Apuseni Mountains started at least 2,500 years ago. Analysis of gold artifacts found throughout the ancient world, including Troy and Egypt, indicate an origin from the Apuseni deposits. Before the Roman Empire, the region was known as Dacia; Emperor Trajan conquered the region in 106 AD. The Romans sacked the Dacian Royal Treasury and hauled off more than half a million pounds of gold and twice as much silver. Presumably, this wealth was originally mined from Apuseni. The mining center during Roman times was Ampulum, which became the modern town of Zlatna. The region bloomed again as a mining center in the 19^th century when the area was under control of the Habsburgs.

The Golden Quadrilateral is rich in tellurium; in fact, the element was first described from samples of native tellurium from here in 1798. Many gold and silver tellurides were first described from here, including krennerite, nagyagite, petzite, stutzite, muthmannite and museumite. Hessite was actually first described in what is modern Kazakhstan (and named for a German chemist that described the mineral in 1829), but by far the best crystals are from Botes. There is very little written on the history of Botes. This is mainly due to the fact that it was a modest mine in terms of metal production, but in terms of hessite production it was truly remarkable!

I have 5 hessites from Botes. Most are like the specimen above—a cluster of crudely cubic grey crystals on matrix with quartz (and usually a little sphalerite). To many modern collectors this specimen has limited aesthetic appeal; however, every one of these specimens has a series of old catalogue numbers and labels written by the hand of long deceased collectors. Botes only produced hessites for a relatively short period in the second half of the 19^th century; all five specimens are “related”. My favorite hessite (pictured below) is a cluster of elongated crystals (the largest blade is 1.4 cm) on a sliver of matrix. The hessite crystals have blebs of gold on their surfaces. The original mineralogical explanation for this assemblage was that petzite (petzite has a formula of Ag3AuTe2, simplistically, a gold atom substituting for every fourth silver atom in hessite) was intergrown in the hessite. However, the most modern explanation is that the gold is actually intergrown directly in the hessite. Either way, the gold blebs are a unique signature.

A visit to the Vienna Museum of Natural History is a reminder to me of why I collect minerals. The minerals are magnificent recorders of past geologic events—ancient subduction zones and strata volcanoes, erosion and rearrangements of continents. At some point the veins that carried the minerals were discovered by a prospector, and eventually mined. Some nameless miner decided to collect a piece of unusual ore, which, in turn, made its way to a collector. Through the years that mineral resided in display cabinets or wooden drawers in storage racks, and may have changed hands many times. Scientists may have studied the sample and recorded the crystal structure or detailed the chemistry and postulated the theory of formation. Today that specimen—a story in stone—is in my collection, but only as a temporary resting place until to passes to the next collector.

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Wandering in the Mountains

Geology, Nature, and Adventure teaching lessons in life