Old Rock Day – January 7

This day is set aside (though no one knows how long it has been observed or when it was first celebrated), to consider how old the Earth is and how it has shaped our lives. It’s also a shout-out to some of the earliest geologists like the Theophrathes, Pliny the Elder, Ulisse Aldovandi, James Hutton and William Smith.

National Jewel Day – March 13

This special day is set aside to appreciate precious stones and jewelry. From the earliest examples of stone, bone, and shell jewelry, to the most lavish and intricate designs of today, National Jewel Day is meant to recognize them all. Those who choose to participate are encouraged to wear their most spectacular bejeweled pieces and take the occasion to gift jewelry to those important people in their life.

Geologists Day – April 7

This day is dedicated to those folks who make it their life’s work to explore, research and disseminate their knowledge of rocks and Earth’s history. It is also the time to appreciate all of those things in our lives that we have or know because of geologists. This includes such daily used items as toothpaste and even cell phones. Younger folks contemplating a career in geology can take this opportunity to discuss with practitioners in the field, what the job is actually like.

Earth Day – April 22

You can’t get any “Earthier” than rocks, gems and minerals. This is a day for rockhounds to explore and to appreciate Earth’s treasures.

Nickel Day – May 16

Devoted to the mined element, nickel, this day was created to acknowledge this important metal. Nickel has been used by humans for at least 2,000 years. By the middle of the 19th century, it was ubiquitous in American coinage as well as that of other European nations.

Dinosaur Days – May 15 & June 1

Dinosaurs lived millions of years ago, but they’re top of mind today. So much is still unknown about these fascinating creatures. Celebrate what we know and anticipate what we don’t on this fun day for young and old alike.

National Caves & Karst Day – June 6

This day is dedicated to the majesty and importance of these amazing rock formations. Most people know what caves are, but few are familiar with “karst” landscapes. A karst landscape is characterized by rocky hills, aquifers, springs, sinkholes and caves. Hundreds of different minerals and gems are found in caves, and 40 percent of drinking water in the U.S. comes from karst aquifers.

World Oceans Day – June 8

Beach finds from shells to rocks, minerals and sea glass are a favorite. Celebrate the oceans that bring us this bounty.

International Drop a Rock Day – July 3

This a day for having a bit of fun while inspiring kindness toward others. Across the world, individuals, families, and groups of all types get creative and paint rocks with pictures, themed messages, or even advertising and hide them. Anyone can try to find them. When they are found, the lucky holder of that rock can keep it, hide it again, or if it is part of a local promotion, contact the sponsoring group. This highly popular activity is not restricted to International Drop a Rock Day; many groups do this throughout the year and hold rock-painting parties before going out and hiding them.

International Rock Day – July 13

Sometimes referred to as World Rock Day, this day is intended to celebrate and to contemplate the importance of rocks to humankind. It is to honor the rock as one of the most fundamental aspects of human survival. If there is one day per year to give rocks their due, this is it!

National Pet Rock Day – September 1

This tongue-in-cheek holiday is dedicated to the 1975 marketing scheme that led to the sale of over one million pet rocks. On this day, many people “adopt” a pet rock at functions planned to celebrate this phenomenon.

Collect Rocks Day – September 16

Held since 2015, Collect Rocks Day celebrates all of the diverse types of rocks and all of the different places they can be collected, no matter where in the world you live. It is a celebration of Earth and geology for everyone.

National Fossil Day – October 16

As the name implies, this day is reserved for appreciating and exploring fossils. Of the approximately 250,000 different fossilized species that have been identified, it is estimated there are millions more to be found. Many groups organize fossil hunts and expeditions on this day in early fall. Be sure to find one near you.

This story about rockhound holidays appeared in Rock & Gem magazine. Click here to subscribe. Original story by Chris Bond. Updated yearly to reflect current dates and holidays. 

The post 2024 Rockhound Holidays first appeared on Rock & Gem Magazine.

Before the Show

Before there was a show in Tucson the city of Phoenix, about 100 miles north, was enjoying a fine annual gem and mineral show hosted by three local clubs: Mineralogical Society of Arizona, Air Research Club and Maricopa Lapidary Society. Advising this group was Arizona’s State mineralogist and Museum Curator, Arthur Flagg.

The Phoenix Show was successful and attracted dealers and visitors from all over the west. After the Phoenix Show, many dealers would drive down to Tucson to visit the wholesale mineral dealers there to stock up. One of the dealers who attended the Phoenix Show, Bob Roots from Colorado, would go to Tucson to buy minerals after the show. He’d stay with Clayton Gibson of the Tucson Gem and Mineral Society. It was Bob in 1954, who urged Clayton to get his Tucson club to have a mineral show.

Humble Beginnings

In April 1955, the Tucson club hosted a small weekend show in the cafeteria of a local school. It was a success and the next year the show was moved to February and to a World War II Quonset hut at the county fairgrounds.

As the show grew, an area for wholesale deals was added when the TGMS expanded the show to include a second nearby building, the nearby cow barn. To use the cow barn, club volunteers showed up with brooms and shovels as there had been a cattle show the past weekend. Talk about a dusty venue! Wholesale dealers had a heck of a time just keeping their minerals clean during that show, and visitors had to deal with a very dusty atmosphere — but the wholesale event was a success!

Two rockhounds who won exhibit ribbons at this first show were Richard Bideaux and Gene Schlepp who became future leaders in the show.

The growing demand by dealers to be in Tucson during show season led to more and more sales in motels and on street corners. One dealer even rented an abandoned gas station across from the fairgrounds to conduct sales. The Holiday Inn, where the TGMS housed visiting lecturers, like Smithsonian’s Curator Paul Desautels, also attracted dealers, and eventually organized satellite shows began to appear.

By 1960, at the suggestion of Dick Bideaux, the club invited Paul Desautels of the Smithsonian to lecture at the show. With the Smithsonian participating the show gained national status in 1961.

Moving to the City

When the Show moved from the fairgrounds to the Tucson Convention Center, the nearby Desert Inn, which is no longer standing, quickly became the evening gathering place. Filled with dealers during show season, it served as a perfect social center, as dealers introduced new finds, friendships grew, and swapping of countless stories became traditional entertainment.

Unexpected Evacuation

A certain new mineral discovery gave rise to one of the more memorable Desert Inn stories. A dealer staying at the hotel had just received a large shipment of superb wire silver in calcite specimens from Batopilas, Mexico. The silver specimens needed cleaning, and the enclosing calcite had to be removed so fine silver wires would show. The dealer, pressed for time, bought gallons of pool acid (hydrochloric acid) and dumped it in his room’s bathtub immersing the calcite and silver specimens. Well, that certainly did the trick! The calcite dissolved, the silver wires were exposed, and as a result, the Desert Inn had to be evacuated because of the noxious fumes.

Another year just before showtime, as dealers were beginning to check into the hotels, a resident who had been convicted of a crime and granted a day to clear up financial affairs checked into the Desert Inn. Fearing incarceration, the man went to his room, climbed into bed, and ended his life.

Of course, the body was removed by police and the mess was tended to and the room cleaned. But, the motel owner, to save money, did not replace the mattress, which was greatly compromised. The mattress was just flipped over, and the room was rented to an unsuspecting mineral dealer. Sometimes the truth is truly more disturbing than fiction.

Elephant Incident

When the TGMS originally took over the Tucson Convention Center for the show, they did not use all of the space, including the arena. While the wholesale sales took place in a large room in the upper level of the center, the Main Exhibit Hall on the ground level housed the show. Next to the building, was the arena, which the city continued to lease or rent out for other events. Sporting events like ice hockey and basketball were held there.

In the early years, it was common practice for events to be booked into the Convention Center immediately before the Tucson Gem and Mineral Show. But one year a serious problem arose.

That year the City of Tucson had booked a circus in the arena just before the Show. When it came time for the circus to move out on a Monday before crews began setting up for the mineral show, tragedy struck. One of the circus elephants died on the arena floor. Can you imagine having to move a deceased adult elephant in a hurry? The crews were able to remove the elephant, after much effort, just in time for the start of the Show. That situation convinced the TGMS Show Committee that it would be best to have the show occupy the arena as well.

Quick Response Relocation

In 2019, the Tucson Show added another chapter to the history of the arena. By this time, the City had given overall management of the Convention Center to a private company. The new management continued accepting bookings at the arena for basketball and hockey games and concerts, just before the Tucson Gem and Mineral Show. Due to this schedule, the hockey ice is commonly left intact on the floor for use, even during the show. In the past, the ice was covered with a wooden deck, so the arena could be used for the Show.

Such was the case during the February 2019 show. The arena floor was solid ice. Naturally, the Tucson Show Committee assumed the ice would be dealt with as usual. But the company managing the convention facility said the ice would remain and would be covered by temporary plywood covering, which required all tables and equipment to be carried in manually. This meant no motorized equipment could be used. How could a mineral show with heavy tables, metal curtain posts, and dealer suppliers be set up on such a weak floor? It was an impossible situation.

This left the TGMS Show Committee with a huge problem. The arena show had to be relocated. So, the Show Committee moved the dealers scheduled to be in the arena into another Convention Center area, the Grand Ballroom, which is off the main Galleria entrance. The American Gem Trade Association Show had ended a day or two before the Tucson Show, and with many sighs of relief, it worked out beautifully.

Last-Minute Ruling Keeps Show on Schedule

Another of the Tales from the Tucson Show archive saw the near cancellation or delay of the show, due to a pending court case. We did not find out until 9 a.m. on the opening day of the show if the court would rule in our favor! Fortunately, the show did open on time, and crowds of collectors entered the convention center to view the superb dealer exhibits.

The cause of this near delay/cancellation happened a year earlier, with a dispute over a dealer contract. Show contracts do not guarantee a dealer any future show space, only for the year of issue. One show dealer was not issued a contract the following year, so he sued to be allowed in. The matter went to court, and on opening day, with all of us standing around waiting, we finally got the phone call that the show could open on time!

Even before the Tucson Show opens each year the local motels are full of dealers. Motel reservations have to be made well in advance, which can be a bit of a challenge for visitors from other countries. As it happened, the curator of the Sorbonne, Paris asked a club member to make him a timely hotel reservation. The club member, fully intending to do it, forgot! When the French guest arrived, the only room available was at a motel named the “No Tell Motel?” Enough said!

The Next Step

At the behest of Dick Bideaux, the show committee invited Dr. Peter Embrey, Curator of the Gem and Mineral Collection at the Museum of Natural History in London to exhibit and lecture. Peter came in 1972 bringing with him a superb display of English minerals.

Full-Time Needs

By now, the show needed an office and a full-time show manager. The Club bought a combination meeting hall and office building. After using several part-time show managers, the club brought in Pat McClain as the full-time office manager. It is remarkable the world’s best-known gem and mineral show functions so well with a small staff and Pat’s firm hand aided by many volunteers.

Politics & Gem Shows

Another factor that played a role in the growth and success of the Tucson Gem and Mineral Show is politics. The adage “it’s not what you know but who you know” applies here. The Tucson Gem and Mineral Society was made up of a group of collectors living in the Tucson area.

One of the most active and influential groups in the City of Tucson is the Mountain Oyster Club. Mountain oysters are a desert dweller’s tongue-in-cheek name for a puma’s manhood. Some family members of this group date back to original Spanish land grants and were very active in business and local politics.

One member was critical in helping me with show publicity and government contacts including the Mayor of Tucson. I was able to work with this group which was a big help as the Show gained status.

Dick Bideaux’s father owned small-town newspapers in Southern Arizona and was a big help with publicity. He was also politically active and well-connected.

The Udall family was active in Arizona politics and through them, we were able to approach the Library of Congress to borrow the Silver desk set and ink well given to Abraham Lincoln by the Governor of Arizona for signing the treaty to bring Southern Arizona into the United States. The silver desk set was made of silver mined in Arizona.

Fabergé Eggs

Show visitors were also in a position to help grow the show. One regular exhibitor collector happened to live next door to Malcolm Forbes, once owner of many Russian Peter Carl Faberge Easter eggs made each year for the Czarina. We proposed to the Forbes Museum, New York, asking for an Easter egg display. They agreed and this also brought the Russian Ambassador to the show. As luck would have it the last living member of the Faberge family, Tatiana Faberge was visiting Phoenix at the time and she brought an exhibit of Faberge materials.

Dedicated Volunteers

The club’s members who volunteered for days, weeks and years were and still are the heart and basis on which the show grows.

This story about how the Tucson Gem and Mineral Show got started appeared in Rock & Gem magazine. Click here to subscribe. Story by Bob Jones.

The post How the Tucson Gem & Mineral Show Got Started first appeared on Rock & Gem Magazine.

Zircon is the mineral zirconium silicate (ZrSiO₄), which contains the elements zirconium, silicon, and oxygen. It crystallizes in the tetragonal system and has a very substantial Mohs hardness of 7.5. With its durability, high index of refraction, and range of pleasing colors, zircon is an attractive gemstone; the colorless variety was once a popular—and sometimes fraudulent—substitute for diamond. 

What is Zircon?

As the most common zirconium-bearing mineral, zircon is widely distributed in igneous and metamorphic rocks. Its extremely durable crystals can survive for billions of years. Because zircon often contains traces of uranium, it is an ideal medium for the radiometric dating of ancient rocks. The oldest known rocks—more than four billion years old—have been radiometrically dated by measuring the extent of the atomic decay of the uranium in tiny zircon crystals.    

Zircon serves as a refractory material in ceramic, foundry, and casting applications. It is also the only ore of zirconium, a soft, ductile, silvery-white, relatively common metal that ranks 20th in crustal abundance.

German chemist Martin Klaproth discovered the element zirconium in 1789. A century later, metallurgists learned that it improved the corrosion resistance of steel.

Because it does not absorb neutrons, zirconium is the preferred cladding metal for fuel rods in nuclear power plants. And because powdered zirconium reacts quickly with oxygen, hydrogen, and nitrogen, it is used to purge traces of gases from vacuum tubes.

What is Zirconia?

The second most common zirconium-bearing mineral, after zircon, is baddeleyite, or zirconium oxide (ZrO₂). Baddeleyite, also known by the industrial term “zirconia,” crystallizes in the monoclinic system. Synthetic zirconia, prepared by roasting zircon at high temperatures, was the mantle material in the first incandescent lamps of the 1880s. By 1900, Nernst-type electric lamps contained zirconia “glower rods” which, when heated electrically, glowed with a brilliant, white incandescence.    

With its high reflectivity, zirconia is used as an opacifier and a pigment in ceramic glazes. Zirconia is also employed in the oxygen sensors that control combustion in gas furnaces and automotive engines.

About 600,000 tons of zirconium (contained in zircon concentrates) are now recovered annually as a by-product of mining titanium-rich sands.

Uses for Synthetic Zirconia

Just as zircon is a gemstone, zirconia (synthetic) also has a gem use. In the late 1960s, researchers working with advanced optical-electronic materials for lasers and computer-chip substrates became interested in zirconia.  They found that when monoclinic zirconia is heated nearly to its melting point of 2690° C. (4874° F.), it passes first through a tetragonal phase and then a cubic phase.

But the cubic phase was unstable and reverted back to its monoclinic form upon cooling. Adding traces of yttrium oxide (yttria), however, stabilized the zirconia in its cubic phase. Known as yttria-stabilized zirconia, or YSZ, this hard, chemically inert, polycrystalline, ceramic material now has many specialized uses in medicine and industry.

Single YSZ crystals, grown in special high-temperature crucibles, are called “cubic zirconia” or “CZ.”  It was first commercially synthesized in 1976. Today, 13 tons of CZ are manufactured each year.

So despite the sometimes confusing similarity of their names, zircon, zirconium, and cubic zirconia have distinctly different properties and fascinating uses.    

This story about are zircon and zirconia the same appeared in Rock & Gem magazine. Click here to subscribe. Story by Steve Voynick. 

The post Are Zircon and Zirconia the Same? first appeared on Rock & Gem Magazine.

Mineral specimens are commonly described as dendritic, acicular, columnar, striated, botryoidal, banded, and prismatic, acicular.

These terms are the direct result of two things, the mineral’s internal atomic structure and the role it plays in a mineral’s development and the effects of the environment on a mineral during formation.

How Crystals Form

Crystals develop because of the electron attraction between metals and non-metals that loan, borrow, or share electrons. This ionic sharing during crystal growth creates an imbalance in electron charges. The imbalance attracts more molecules during crystal growth.

The attraction does not extend in all directions. This can determine the direction of growth. If the crystal growth is dominant in one direction, growth develops into a prismatic form we see in tourmaline and quartz. If growth is exclusive to one direction, the crystals are needle-like, which we see in some zeolites, rutile and some stibnite.

Native Copper

When we describe a mineral, we may start by naming its crystal system. But we need to use terms that describe the specimen in far more detail by describing the mineral’s crystal habits. Native copper is an example of this. It is a cubic or isometric mineral.

Cubic copper crystals that have six faces are very uncommon. More common are copper crystals that form as a twelve-sided dodecahedron. In this form, it can almost look like a rounded ball when the faces are tiny.

Most frequently, we find copper in an arborescent or dendritic crystalline form. This develops because of environmental influence.

In a rich solution, as the copper crystallizes rapid molecular electric attraction and growth can create slight irregularities in the unit cells. This causes repeated branching and elongation of the crystallizing copper and arborescent growth. If the growth space is restricted to two dimensions as in a narrow crack, a dendritic form emerges.

Time, Pressure & Temperature

High heat, where crystals form, also determines the formation. Some crystals develop from vapors. Others form in solid rock while it is in a fluid or plastic state. This allows molecules to slowly migrate toward each other and connect to form a crystal.

The majority of minerals form in watery solutions that vary widely in mineral content, richness, temperature and pressure. Even the direction the solution is moving can influence how a crystal grows and what form it takes.

Mineral deposits are always described as low, medium or high-temperature deposits. This is important as that energy has a profound influence on what species crystallize out of a solution first.

Each species has its own temperature of crystallization. Some species form first in a pocket or open seam followed by crystals that form at a lower temperature.

Zeolites are late-forming species. They are often found having formed last in a cooling pegmatite pocket full of species that formed first at higher temperatures.

Formation Preferences

If you handle enough mineral specimens, you learn which minerals prefer a particular crystal growth habit. For example, stibnite is always found in long slender needle-like crystals. This indicates rapid or more persistent growth in one direction because of molecular attraction.

Gem tourmalines are almost always striated because of oscillatory growth. This happens when two different crystal forms vie for dominance.

Hematite, on the other hand, is often found in a botryoidal form. It has a penchant for very rapid growth forming radiating needles from a common starting point.

Malachite prefers to form in velvety needle coatings rather than in discrete lengthy prisms. The discrete prisms are the common habit of many species like epidote, kyanite, beryl, and quartz.

Calcite’s Unique Crystal Growth

One of the most interesting common mineral species to demonstrate crystal growth habits is calcite. It is found in every mineral environment with both low and high temperatures and climates. It is also found in near-surface sedimentary deposits and much deeper locations.

Because of this, calcite manages to develop in at least five basic crystal forms. This is one reason why collecting calcite is widespread and varied.

These different crystal forms, all in the hexagonal-trigonal system, have their growth controlled mostly by the temperature of the environment. The five basic forms calcite takes in crystals are scalenohedrons or dog tooth, tabular, simple hexagonal, rhombic, or disc-like or poker chip form. They are all hexagonal but are not always easily recognized.

Higher temperature solutions are prone to developing calcite that has a scalenohedral or poker chip form. Slightly lower temperature solutions produce calcite crystals with a tabular calcite crystal form. In somewhat lower temperature deposits, simple hexagonal calcite occurs. Rhombic crystals can form from solutions where the solution temperature is at ambient levels.

Solutions around 25°C and lower produce dog tooth crystals. These are common in near-surface sedimentary deposits. This explains why we find small rhombic and dog tooth crystals common in midwest limestone deposits.

This does not mean a particular deposit produces one crystal habit exclusively. Temperatures within a given deposit can vary over time, producing different crystal habits.

Fluorite Crystal Formation

Another popular mineral that shows a wide variation in crystal form is fluorite. A major influence on the form of a fluorite crystal is the interplanar distance, which is affected by the energy available during crystallization.

As in calcite, and other species, the variation from low to high energy also affects the complexity of the fluorite crystal formation.

As it happens, octahedrons of fluorite require less energy to form, so we find them as a common form of this calcium fluoride. Cubes require more energy, which is why it is not uncommon to find both octahedrons and cubes of fluorite in the same deposit.

Deposits producing fluorite from higher temperature hydrothermal solutions will produce slightly more complex dodecahedrons. In very high-temperature metal deposits, more complex fluorite crystals are found, some with as many as 24 or even 48 faces.

Molecular Attraction & Crystal Growth

Hopper crystals are good subjects to use to explain molecular attraction and crystal growth. A hopper crystal starts out growing in a solution in a normal way. It attracts like molecules to itself once it starts to grow.

Growth continues consistently but stops when there are no molecules of the mineral left in the solution. This happens with a hopper crystal before it can complete itself. As the molecules are attracted to a growing crystal, they attach sequentially from the prism faces inward. They are not growing from the inside out. They grow from inward.

Molecules first attach to the top outer edge of the growing crystal then continue the growth by filling in the spaces. A sudden stop in the availability of molecules leaves the crystal with a partially filled crown. In some cases, lack of molecules results in crystals around the top edges of the prism faces and leaves the center of the termination unfinished.

Imperfections in Crystal Growth

There are other factors, such as imperfections, that can influence crystal growth. All it takes is one atom or molecule to fail to fit precisely where it belongs and the result can be a change in growth. Sometimes the imperfection marks the beginning of another crystal.

Rhodochrosite exemplifies this process. It forms in layers or bands, as well as stalactites. A change in the composition often takes place as impurities may enter the solution
during the deposition process.

Botryoidal minerals like malachite, hematite, and smithsonite tend to grow a myriad of crystals, rather than a single or small cluster. They develop spherulites around points of nucleation. These tiny clusters of molecules attract like molecules equally from all directions. This process allows many small crystals to form at the same time. Fan-like growths developing next to each other are common.

Crystal growth habits are an integral part of our ability to identify a mineral. After all, crystal habits are what make mineral collections more interesting.

This story about how do crystals grow previously appeared in Rock & Gem magazine. Click here to subscribe! Story by Bob Jones.

The post How Do Crystals Grow? Exploring Crystal Habits first appeared on Rock & Gem Magazine.

Rock art, which is defined as ancient, man-made markings on natural stone, is a global phenomenon that spans thousands of years, divergent cultures and entire continents.  Because pictographs and petroglyphs are artifacts that offer insight into the symbols, religious and belief systems, and origins of abstract and figurative art of past cultures, they are usually considered in an archaeological context.

Art and Minerals

But no less interesting is the mineralogy behind rock art—specifically the pigments utilized in pictographs and the rock varnish into which most petroglyphs are engraved.

Rock art is found throughout North America, but is most abundant and prominent in the arid, exposed-rock landscapes of the greater Southwest, including Southern California, Arizona, Nevada, New Mexico, Utah, Colorado, and western Texas, where thousands of sites are decorated with pictographs and petroglyphs.

Arizona’s federal lands alone have more than 2,500 rock art sites, a few with only a single image, others with hundreds and even thousands of images. The largest rock art concentration in the Western Hemisphere is in Southern California’s Cosos Mountains, where basalt cliffs are adorned with more than 100,000 petroglyphs. Utah has at least 7,000 rock art sites, while New Mexico’s Petroglyph National Monument alone has 25,000 petroglyph images.

While rock art images are prehistoric artifacts, they have nevertheless had a profound influence on contemporary Southwestern art and culture. New Mexico’s state flag design, a sun with four rays representing the four directions, four times of day, four stages of life, and four seasons, is taken from a Zia petroglyph. Rock art images of lizards, howling coyotes, bighorn sheep, and sun spirals are popular motifs in everything from modern wall hangings and pottery designs to coffee cups, lawn ornaments, and corporate logos.

Iconic Southwest Rock Art

Perhaps the most celebrated rock art image is that of “Kokopelli”, the flute-playing, hunchbacked Hopi deity of reproduction and music, which has evolved into an immediately recognizable, graphic symbol for the entire Southwest.

While archaeologists and anthropologists ponder the purpose and meaning of rock art, mineralogists study its physical features. In the North, Midwest, and East, Native American artists used hard, quartz-based rocks to engrave petroglyphs into relatively soft limestone and sandstone surfaces. A well-known example in the East is Dighton Rock, a 40-ton sandstone boulder covered with deeply carved petroglyphs that is now displayed at Dighton Rock State Park in southeastern Massachusetts.

But in the Southwest, petroglyph artists engraved sandstone only occasionally, performing most of their work instead on far harder rocks such as basalt, which is common in the regional deserts and canyons. These shallow engravings depend not on depth for their visual impact, but on color contrast. The critical element in Southwestern petroglyphs is rock varnish, the thin, dark coating that forms on rock surfaces over long periods of time.

Rock varnish is most familiar as the dark, vertical stains that dramatically decorate canyon walls and cliffs throughout the Southwest.

Examining Rock Varnish

German geographer and explorer Alexander von Humboldt made the first historical mention of rock varnish in 1799 when he visited Venezuela and wrote of granite boulders that appeared “smooth, black, and as if coated with plumbago”. At the time, plumbago referred to graphite, a black, crystalline form of elemental carbon. Indigenous tribesmen told von Humboldt that the hot, tropical sun had burned the boulders to blackness, one of the many early guesses as to the origin of the strange coating.

Similar coatings observed on rocks worldwide became the subject of a mineralogical mystery that lasted for nearly two centuries. Early theories about the origin of rock varnish ranged from deposits left by ancient seas, residues of decomposing organic matter, and the chemical “rusting” of rock surfaces. By the late 1800s, mineralogists began focusing on a process in which the sun and heat supposedly caused mineral-rich water to “sweat” out of rocks, evaporate, and precipitate a dark mineral coating.

By the 1920s, mineralogists suspected that rock varnish consisted largely of iron and manganese oxides, a theory that could not be proved because the oxide particles were too fine to be studied by the analytical methods that then existed. Some mineralogists even proposed the innovative idea that rock varnish formed when direct sunlight somehow combined with microbial action to cause dark-colored iron and manganese oxides from the interior of rocks to concentrate on their surfaces.

That idea persisted until the late 1970s, when advanced analytical methods, coupled with some brilliant, scientific detective work, finally unraveled the mystery of rock varnish’s origin. In the first step, researchers determined the actual composition of rock varnish. It was found to be a thin coating only a tiny fraction of a millimeter thick—about that of a human hair—consisting of 60% clay minerals and 20 to 30% iron and manganese oxides, the latter mainly birnessite (hydrous sodium calcium manganese oxide), goethite (basic iron oxide), and hematite (iron oxide). The remaining portion is a mix of some 30 minor compounds.

Influence of Manganese on Varnish

Researchers also learned that the manganese content of rock varnish was as much as 100 times greater than that of nearby rocks and soils, and that high concentrations of manganese-based minerals created rock varnish’s dark color. Rock varnish with high levels of manganese oxides is nearly black; lower levels of manganese oxides (and thus higher relative proportions of hematite) produced a brown or orange-brown color.

Researchers then attempted to piece together the origin of rock varnish. In 1979, Arizona State University professor of geography Dr. Ronald Dorn and his colleagues employed scanning electron microscopy on hundreds of rock varnish samples from different sources. All specimens were observed to contain manganese-concentrating bacteria of the genus Metallogenium, a find that suggested a biological origin for rock varnish.

Again employing scanning electron microscopy, Dorn and his researchers discovered a distinct morphological boundary between the rock-varnish coating and the host rock. This absence of any compositional gradient showed that rock varnish is actually an accretion of materials that originates not from the interior of the rock, but which accumulates from extraneous sources. This discovery was the final piece of the puzzle that explained the origin of rock varnish.

Rock varnish begins to form when fine, wind-blown clay particles and smaller particles of iron and manganese compounds gradually collect on rock surfaces to form thin, porous films. Manganese-concentrating bacteria then absorb and oxidize the metal-bearing particles, precipitating black manganese oxides and reddish-black iron oxides.

Mineral Conversion Contribution

In a complex relationship of water, clay, bacterial action, and mineral compounds, water migrates through tiny pores in the clay, transporting mineral compounds. Metallogenium bacteria convert the iron and manganese compounds into oxides. Along with organic products of bacterial oxidation, these oxides combine with the clay particles to create a durable cementing agent that adheres tenaciously to rock surfaces. This thin, but steadily developing, rock varnish layer shields the bacterial colony from desiccation and intense solar radiation, enabling the layer to eventually build to its full thickness.

Researchers then formally named the dark rock coating that they had investigated. Since the time of von Humboldt, this coating had been variously known as “rock black”, “rock rust”, “rock patina” and, most popularly, “desert varnish”. To dispel the erroneous idea that this coating only formed in desert regions, researchers agreed upon the term that is preferred today: “rock varnish”.

Different rocks have varying abilities to accept and retain rock varnish. Limestone rarely only exhibits rock varnish because it is too water-soluble to provide a stable surface on which the coating can form. The densest and most durable rock varnish forms on basalt, rhyolite, granite, quartzite, and other similar rocks that are highly resistant to weathering.

Although a fully developed rock varnish layer is tissue-paper thin, it can nevertheless alter the color of cliffs, boulder fields, and even entire mountains. On a smaller scale, it can completely disguise the surface appearance of individual rocks. Even a thin layer of rock varnish can make light-colored granite and rhyolite look like dark basalt.

Techniques To Create Petroglyphs

Petroglyphs are created by removing selected areas of dark rock

varnish to expose and contrast with the lighter-colored, underlying rock. Petroglyph artists employed four basic techniques. In “pecking”, they repetitively struck rock surfaces with naturally pointed or flaked stone tools. In “drilling”, they rapidly rotated flaked stone points mounted on wooden shafts. “Scratching” utilized simple back-and-forth movements with sharp stone points; “grooving” was a more precise and deeper scratching technique.

Rock varnish will eventually reform on engraved areas, gradually reducing the contrast of petroglyphs. But because rock varnish develops so slowly, petroglyph images last for thousands of years.

Attempts to date petroglyphs by absolute (direct) and relative (indirect) methods have had only limited success. Direct dating focuses on the growth rate of rock varnish. In the Southwestern climate, a full layer of rock varnish accumulates in roughly 10,000 years.

This makes it possible to roughly estimate the age of the partial coatings on engraved petroglyph surfaces. Unfortunately, the rate of rock-varnish development varies significantly with local climactic or other environmental conditions.

A somewhat more precise dating technique is cation-ratio dating, which determines and compares the degree of leaching of iron, manganese, calcium and potassium cations.

Rock Varnish Helps Date Art

Comparing the degrees of leaching in fully developed rock varnish layers with those in the partial layers on engraved petroglyphs gives a rough idea of when the engraving was made.

Knowing the approximate age of rock varnish not only helps archaeologists date petroglyphs, but also enabled geologists to date such landform-altering events as landslides, glacial movements, and volcanic eruptions.

In relative dating, archaeologists attempt to link petroglyphs to nearby cultural ruins or artifacts of known age—a technique that assumes that the petroglyphs and nearby artifacts or ruins are actually related. Conclusive relative dating is valid only with representational rock art images, such as those depicting Christian crosses and horses, which were obviously made after the Spanish arrived in the Southwest.

Unlike engraved petroglyphs, pictographs are paintings on rock, usually sandstone or limestone with smooth, light-colored, fine-grained surfaces. And while petroglyphs were made in exposed areas, pictographs are found only in cave interiors, on canyon walls, or at the semi-sheltered bases of cliffs, indicating that pictograph artists were clearly aware that their work was vulnerable to direct exposure to the elements.

Pictograph paints consisted of a pigment, a binder, and a fluid. The pigments were minerals, carbonaceous fire residues, clay or shell, all ground to a fine powder. The primary pictograph colors were red, black and white; yellow and blue-green were much less common.

Hematite Headlines Pictographs

The predominant pictograph color is red, which is not surprising considering its high visual impact and the plentiful supply of the hematite, or iron oxide. While the color of crystalline hematite is silvery-gray to near-black, that of particulate hematite is red. The finer the hematite particles, the more intense and bright is their red color. Hematite is chemically stable, impervious to the action of natural acids, and does not fade in sunlight. Red hematite pigments were used extensively in pictographs around the world, most notably in the famed, 30,000-year-old Neolithic cave paintings of southern France.

Black, the next most common pictograph color, is derived from pigments of elemental carbon obtained from fireplace soot or finely ground charcoal or coal. Some black pigments consist of finely ground pyrolusite (manganese dioxide) or similar manganese oxides or hydroxides. Both elemental carbon and manganese oxides are chemically stable and produce jet-black paints.

White pictograph paints contain finely ground white clays, seashells, bones, gypsum (hydrous calcium sulfate), and caliche (a natural calcium-carbonate cement that often coats rocks in arid regions). White pictograph pigments had varying degrees of chemical stability.

An occasional pictograph color is yellow, which is based on a pigment of limonite or ocher, an abundant mixture of hydrated iron oxides.

Regional-Specific Colors

Blues and greens, which are rare in Southwestern pictographs, are largely restricted to regions with outcrops of the green and blue copper carbonate minerals malachite and azurite. Malachite pigments are fairly stable, but those of azurite are not. Because slow, natural oxidation converts azurite into malachite, most of the blue, azurite-based pigments in pictographs have turned to green.

Organic binding agents in pictograph paints—plant extracts and resins, egg whites, and animal fats, to name just a few—enabled the pigments to adhere to rock surfaces. Water gave pictograph paints their proper consistency.

After they were painted, pictographs eventually became covered by thin veils of white or colorless minerals that were naturally deposited by water that trickled down the rock walls. Originating as dew, rain, snowmelt, frost, or seepage from the rock itself, this water carried varying amounts of dissolved silica and calcium. As the water evaporated, it deposited a mineral film called “silcrete”, which is similar to the hard-water deposits that accumulate on plumbing fixtures.

Silcrete can become so thick that it obscures pictographs, but most often it provides a transparent covering that protects the pictograph and helps to fix the pigments to the rock. Under electron microscopes, pictograph cross sections appear as layers of paint “sandwiched” between two silcrete layers. The original silcrete layer, present before the pictograph was made, adjoins the rock surface. Next is the paint itself, atop which is a second, protective silcrete layer that was deposited after the pictograph was made.

As with engraved petroglyphs, attempts to date pictographs have brought only mixed results. Even the results of radiometric, carbon-14 dating of the organic binder materials in pictograph paints are unreliable. The problem is not the carbon-14 method itself, but in being certain that the tiny organic samples in the paints reflect the actual time period in which the pictographs were created.

Impact of Deterioration

While remarkably durable, rock art is not indestructible. Deterioration,

which occurs with each passing year, is both natural and man-made. Natural chemical and physical weathering breaks down rock surfaces and pictograph paints, while new growths of rock varnish slowly obscure petroglyphs.

Man-made deterioration, both unintentional and deliberate, takes a greater toll on rock art. A major form of unintentional deterioration is industry-generated acid rain. But even touching pictographs and contaminating them with skin oils can alter the delicate chemistry of the ancient paints.

Saddest of all is the destruction of rock art by vandals and “collectors” who deface images, attempt to chisel out or otherwise remove them, or “enhance” them with modern marking materials. This situation has become so serious that the policy of federal land-management agencies is now to reveal only the locations of rock art sites that are regularly patrolled. All rock art on federal lands is protected under the Antiquities Act of 1906. States have similar protection laws.

Although we now understand how rock art was made, the question of why it was made remains unanswered. Stylized animal images appearing together with anthropomorphic figures holding weapons were once logically thought to depict hunting-related events.

Symbolism in Pictographs

Geometric images such as circles were thought to be solar or lunar symbols tied to seasonal or astronomical cycles. Lines or combinations of lines were assumed to represent trails, terrain features, and territorial boundaries, or were interpreted as clan symbols or mnemonic devices for important events.

Some early archaeologists even considered rock art to be nothing more than ancient graffiti, an idea now firmly rejected on the grounds that creating images that would endure for centuries or even thousands of years was not a casual activity, but a thoughtful project that demanded a major commitment of time and effort. Many pictographs are often located in nearly inaccessible areas high on cliffs or cave ceilings—places that would not interest casual artists.

Anthropologists now generally agree that most rock art was created by shamans, whose motivations were spiritual and often enhanced by hallucinogenic trances. All ancient Native American cultures employed rituals, magic and spiritualism to explain nature’s many dualities, such as life and death, day and night, and summer and winter. Rock art can thus be explained as graphic expressions of belief systems that were established in attempts to control these dualities.

While their exact meaning may always remain uncertain, we at least understand the basic mineralogy behind the Southwest’s countless rock art images.

This story about how are petroglyphs made previously appeared in Rock & Gem magazine. Click here to subscribe! Story by Steve Voynick.

The post How Are Petroglyphs Made? first appeared on Rock & Gem Magazine.

Before exploring crystal twinning, it’s important to know how to identify quartz and have an understanding of the quartz mineral group. Crystals can twin in parallel, or routine ways, involving two crystals, or as in complex twinning, several crystals. This is different than inclusions in quartz. To be considered as twins, the crystals must be in a fixed identifiable relationship to each other. As crystals grow in solution, individual ions of a mineral gather to form a crystal. This is an orderly geometric process that produces a pattern that results in an external crystal form.

Influences on Crystal Growth

Several factors influence how crystals grow, one being the direction of flow of the solution. This direction brings ions in contact with the growing crystal from a path that can influence growth. Such direction causes ions to accumulate on the side that receives the flow. This development can affect the orderly process of crystallization.

Sometimes, as the ions move to take a position in the crystal lattice, one ion may not quite fit right, appearing slightly offset. This occurrence is not enough to disturb the lattice structure but can affect later arriving ions.

Under rapid crystal growth, the next arriving ions attach to the slightly offset ion. When this happens, this offset results in a second crystal that grows in a different direction determined by the orderly rules of crystal growth.

The original crystal continues to grow during this time and so does the second attached crystal. This results in two crystals sharing a common boundary, or face, and a singular lattice.

The crystals attach at a predictable angle to each other. We can measure that angle to prove the pair of crystals is twinned. Specimens with such crystal structures are called contact twins, which is just one of several types of crystal twinning. Contact twins involve two crystals, while more complex twins involve several.

Crystal Angles

Crystal twins share a lattice and a face, giving a flattened look. The key to a twin is the distinct, exact angle between the two crystals, called the reentrant angle.

In contact twins, the reentrant angle appears as a ‘V’ notch that can range from barely visible to a wide-open span. This often makes the two crystals look like rabbit ears. The reentrant angle is always the same degree of separation.

This is critical to identifying a twin because there can be many “paired” crystals that look like contact twins. Unless the angle between the two quartz crystals is 84 degrees, they are not twinned.

This type of quartz twin is called a Japanese law twin. Regardless of how many Japanese twins you examine, there is a constancy of that angle. Other species twin with different reentrant angles, but each remains exactly constant to that particular species. Contact twins are common in quartz, gypsum, calcite and some feldspars like albite.

1. Types of Crystal Twinning – Penetration Twins

A second twin form of minerals is penetration twins. Simply described, penetration twins are two crystals of the same mineral that look as if they have been shoved together.

Penetration twins occur when one crystal starts to develop, and a second crystal starts to grow inside the first as ions offset along an axis of the first crystal.

The second crystal grows at a different angle, determined by the direction of the first crystal axis. The result is one crystal resides within another crystal with the corners of the second crystal protruding from the center of each host crystal’s face.

This formation is prevalent in cubes of fluorite as well as pyrite. Note both these species are in the isometric or cubic crystal system, which commonly develops penetration twins.

Isometric Crystals

Isometric crystals also form octahedral crystals. Why is this important to note? Because the two cubic crystals in a penetration twin share a common octahedral axis as part of a valid twin formation.

Staurolite, a monoclinic crystal form, can exhibit a perfect cross twin. Again, a common axis has to be shared for this to be a real cross and twin. In this formation, the same mineral forms another twin when one crystal is at a diagonal 60-degree axis of the host crystal.

Penetration twins can be visualized as one crystal mysteriously passing through another. Mother Nature is mysterious but not magical. Penetration twins are a matter of ions in geometry.

A spinel twin crystal, whether it is spinel, copper, sphalerite, or other cubic minerals, has to appear as an octahedron crystal cut in half. One half of the octahedron is rotated 180 degrees and re-attached to the other half. This process forms two very distinctive angular terminations at opposite ends of the crystal. It creates a visible shallow contact boundary running the length of the twin.

2. Types of Crystal Twinning – Cyclical Twins

One of the most beautiful types of crystal twinning is cyclical twins. They are part of the polysynthetic group of twins. Cyclical twins require as many as six, or eight, crystals to join a flat-sided round donut-like shape. In some cases like aragonite, the cyclical twin has no doughnut hole. Others, like chrysoberyl, have a center hole the crystals twin around.

Cyclical twins only form in the hexagonal, tetragonal or orthorhombic systems. This information sometimes helps identify an unknown mineral.

Cyclical twins develop when several crystals share axes and faces during growth. They attach side by side as each pair forms at an angle to its neighbor resulting in a complete link to form a rounded or cyclical crystal twin.

3. Types of Crystal Twinning – Polysynthetic Twins

Cyclical twins are part of the group known as polysynthetic twins, also known as repeating twins. In the feldspar family, polysynthetic twinning is common, but each crystal is hardly distinctive. Feldspars, such as labradorite and albite, are typically polysynthetic twins.

In these minerals, flat, wafer-thin crystals form side by side, alternating one against the other, resulting in a solid mass. The result is something substantial that a lapidary can use. The beauty of this twinning is that the piece acts as a diffraction, so its component colors are visible. This subtle rainbow effect is referred to as the Schiller effect.

The Schiller Effect

The most fantastic use of feldspars I’ve seen with a Schiller effect resided within the Kremlin. The grounds behind the Kremlin walls feature a riot of flowers in huge planters with large blocks of stone forming low retaining walls.

These blocks caught my eye because each was composed of lapidary gem material. One wall was sensational, as it featured huge blocks of polished labradorite that shimmered in the sun. Unfortunately, my camera was “borrowed” by security during our visit.

Crystal Habit Awareness

One of the real joys of collecting minerals is to be familiar with crystal habits. Not only to recognize but to collect crystals that are a bit unusual. Knowing ‘what’ and ‘why’ such twin crystals form is always a job, but highly rewarding. The more effort you put into learning about and collecting twinned crystals, the more enjoyable your collection will be.

Just a word of caution: Be cautious of crystals that look similar but are not twinned. Crystals that grow parallel, or jut in an angle resembling rabbit ears, may not be twinned. These are things you’ll learn to identify as you develop an interest in twinned crystals.

This story about types of crystal twinning previously appeared in Rock & Gem magazine. Click here to subscribe! Story by Bob Jones.

The post Three Types of Crystal Twinning first appeared on Rock & Gem Magazine.

We have cherished gold since the first human picked up a yellow nugget. We have given it value, gone to the ends of the earth searching for it, and dug the deepest mines to collect it. People have acquired it just to own and admire it for its value, color, crystal form, and aesthetic beauty. You may think by now we would have dug all of this precious metal. Not so!

An amazing find on Father’s Day, 2018 in Western Australia added pounds and pounds of gold to the Earth’s still-growing horde. This is the first in a series of three articles wherein I will explore two great museum gold collections in the Harvard Mineralogical and Geological Museum and the Denver Museum of Nature and Science. Also, we will also examine what Australian miners term a ‘miracle gold find,’ a true horde of gold in quartz.

Every major museum boasts a collection of crystallized gold. Among the more spectacular and better-known museum gold collections in America are not in California, but in Denver, Colorado and Cambridge, Massachusetts. In both instances, I was lucky enough to handle and photograph the best of these collections.

The Harvard’s Burrage Gold Collection is the focus of this article, and in Part Two (appearing in the February 2020 issue of Rock & Gem) I will describe the amazing Australian discovery of millions in gold in quartz, In Part Three, scheduled to be published in the March 2020 issue of Rock & Gem, we will return to museum collections to examine the marvelous crystallized gold collection, featured in the Denver Museum. If all goes well, the public will be able to see some of the Father’s Day gold from Australia once again, at the Tucson Gem and Mineral Show.

Classic Collection

The stunningly beautiful crystallized gold collection at Harvard has a delightful history. The Harvard staff is to be congratulated as they have often shared the best of the collection with the mineral collecting public at major shows like Tucson. I am personally indebted to Dr. Carl Francis, now retired Harvard curator, who gave me permission to examine and take photos of many of the Burrage gold specimens in his office.

To get the collection where I could photograph it we had to bring it out of a bank vault. With two flight bags, we hiked across Cambridge Commons to the bank. We filled the flight bags with millions in gold and hiked back to Carl’s office. I doubt few collectors have walked the streets of Cambridge, Massachusetts, carrying flight bags holding millions in crystallized gold.

The core of the Harvard gold collection was assembled by lawyer industrialist A.C.Burrage, Harvard class of 1883. He had a large mineral collection, including the Georges de la Bouglise gold collection, bought in 1911. That collection has an impressive worldwide array of gold, and also boasts a rich collection of Bisbee azurite and malachite.

Burrage worked as a lawyer but later got into copper mining and made a small fortune, some of which he used to collect superb crystallized gold. The bulk of his collection is from California but, thanks to Bouglise other countries like Australia, France, Russia are represented.

Some of the Harvard gold is so unique they have been given names like “Papillon,” “Butterfly,” “Antlers,” and “the Fan.” Most impressive is the world’s largest ram’s horn of wire gold, properly named “Ram’s Horn”. This beauty has been featured in countless books and articles and displayed at shows as the world’s finest example of a gold ram’s horn.

The Ram’s Horn is an amazing example of crystal growth that extended primarily in one direction. It looks like a bundle of thick yellow wires that start from a gold base, and then the wires grew to create a one inch thick, tapering four and a half-inch long curving horn, with a cute little curl termination. Weighing 263 grams and measuring four-inches plus in length, it is the largest known ram’s horn gold and is considered priceless.

For years those who have admired and handled the Ram’s Horn, including this writer, all have wondered if the piece is pure gold or, like all naturally occurring gold, have a measurable amount of another metal in it like silver. Gold can naturally alloy with other metals including copper, but is most often alloyed with silver. For years to determine the gold-silver content of a specimen, it required damaging the piece to obtain a bit of gold for testing. A less accurate test is to streak the gold on a black rock slab to see its yellowness.

Testing the Ram’s Horn Gold

So, testing the Ram’s Horn was not done until recently when it was taken to Los Alamos National Laboratory, where it could be bombarded with radiation without damaging the piece. The results were very interesting as the tests showed the Horn is up to 30 percent silver. That is not surprising as the silver content of Colorado gold, the source of the Ram’s Horn, tends to run high in silver.

Most of the gold in the Burrage-Harvard gold collection is from California, which often has a silver content of around 90 percent.

The Ram’s Horn actually formed in a gold-copper mine in a Colorado. The piece was found in the now-closed Ground Hog mine, Battle Mountain, Eagle County, Colorado. You may see the mine also listed as within the Red Cliff or Gilman districts. The Horn was described in a Colorado newspaper in 1893 and since that time has become well known around the world. It did not become part of the Harvard collection until 1947 when it was donated. In the 1990s, I enjoyed photographing it in Carl’s Harvard office.

Having a silver content of up to 30 percent is high but not exceptional for a gold specimen. I doubt we have ever found natural gold that is 100 percent gold. California and Colorado gold tend to include anywhere from 10 to 15 of silver content. Of course, every deposit can vary, so silver content in gold for a general area is only an average. Australia boasts some gold that runs very low in silver content. The gold percent of specimens from ‘Down Under’ has been as little as three or four percent silver content. Gold from Romania probably has the highest silver content. Some of it has so much silver it is actually called electrum and has a very pale yellow to a silvery color. There is no exact gold-silver percent to label a specimen as electrum, but some descriptions suggest a silver content of 45 percent or more qualifies as electrum. The ancients used to streak a gold specimen to visually see its color to determine gold and electrum. Streaking is a fairly good indicator to determine value, while also revealing fakery. The Harvard Ram’s Horn is a fine yellow color and is truly a gold specimen.

My favorite gold in the Harvard collection is not the Ram’s Horn, but a small cluster of well-crystallized gold, the Antlers. By itself, it would just be a nice specimen. But, rising up from a solid base of crystallized gold are two nearly parallel slightly curved rods of gold crystals. They stand a couple of inches high, are brilliantly lustrous, and show bright crystal faces along each rod. How these “Antlers” developed as they did is a wonderfully curious event.

Enchanting Gold Crystals

Another intriguing specimen looks like someone has taken a hammer to it and flattened what should be a nice straight line of three-dimensional octahedrons with triangular faces. Instead, these crystals are strung together as a flat, straight row of diamond-shaped crystals. The color is fine, as is the luster. Properly mounted it would make a lovely and very colorful pin. Another crystal is a one-inch cube that shows what I call “oscillatory growth.” As the crystal developed, it could not decide if it wanted to be a cube or dodecahedron, so it grew with alternating crystal faces switching from cube to dodecahedron, to form an intriguing stepped growth crystal with rounded edges. This crystal form is most interesting.

Another very attractive specimen is one I call “The Fan”. It is a relatively flat array of interlocking filigree gold crystals that have formed a hand-sized array of bright gold crystals. It is only one crystal width thick, but over five inches wide with a flat fan-like terminating form. Originally “The Fan” was said to be from Alaska but is actually from the Alaska mine, located in California.

The “Papillon” or “Butterfly” was from the de la Bouglise collection, hence its French name. You don’t need much imagination to see a butterfly when looking at this really attractive gold specimen. The specimen is from Tuolumne County, California and measures about 12.5 cm across. It consists of a solid quartz core or centerpiece, representing the insect body. Spreading out left and right from the quartz are bright flattened and slightly curved gold octahedrons that suggest the wings of the butterfly. Small crystalline gold forms where the head of the insect would be. All in all, it is a very attractive piece and a fine example of crystallized California gold.

The collection also has gold from foreign countries and other U.S. sources. One of the more famous sources of gold in Colorado is Farncomb Hill, Breckenridge, Colorado. If fact, in part three of this series of articles, I will describe the Denver Museum’s gold collection, which is largely crystallized Farncomb Hill, Breckenridge gold. I spent a couple of summers with my family in Breckenridge but had little luck hunting gold, but we did enjoy horseback riding at 10,000 feet.

Farncomb Hill’s Claim to Fame

One mine on Farncomb Hill, the Wire Parch, is famous for its wire gold. Prospectors found masses of crystallized wire gold weighing many, many ounces. The Harvard collection has a lovely six-inch inter-grown cluster of gold wires, all reticulated twins intersecting to form a network of fine delicate crystals. The specimen is more or less flat, about four by two inches without matrix. It is an excellent example of Farncomb Hill gold.

The Harvard collection has several fine gold specimens from other countries worthy of mention. It boasts the largest gold nugget ever found in France, a smooth water-worn mass weighing 509 grams! French Guiana is represented with quartz and crystallized gold weighing 296 grams. The famous Australian gold source of Ballarat is represented by a nicely crystallized gold in Harvard collection. Clearly, a visit to the Harvard Museum should be on your bucket list. The gold specimens are only part of this superb public facility.

The post Famous Gold – Part I: Exploring the Harvard Collection first appeared on Rock & Gem Magazine.

In much of the world, the 1993 blockbuster movie “Jurassic Park” and its unending sequels have become synonymous with the word “dinosaur.” But in western Colorado, the word “dinosaur” is better associated with the town of Fruita and its surroundings.

Located ten miles west of the city of Grand Junction and not far from the Utah line, Fruita is a real “Jurassic Park” and a must-see destination for anyone interested in dinosaur paleontology.

An imposing, 20-foot-tall, forest-green dinosaur looming over the town square reflects Fruita’s pride in its paleontological heritage and history. This model, an accurate, life-sized depiction of Ceratosaurus magnicornis, a Tyrannosaurus-like predator, is Fruita’s official “town dinosaur.” Along with many other dinosaurs, its fossilized bones were found and excavated only a few miles away.

Showcasing Western Paleontological Remnants

Not to belittle Fruita’s town-square Ceratosaurus, but other nearby dinosaur-related attractions are far more impressive. Among them are an outstanding dinosaur museum, several paleontological research areas with hiking trails and interpretive signs, historic and active dinosaur-bone quarries, opportunities to accompany paleontologists on dinosaur-fossil digs, and even a national monument that showcases the region’s spectacular geology.

Fruita’s adventure with dinosaurs began in the late 1890s, shortly after a series of remarkable western fossil discoveries, mainly in Colorado and Wyoming, had transformed dinosaur paleontology from an obscure academic pursuit into an exciting and dynamic science with a large public following. These landmark discoveries had all occurred within exposures of the Morrison Formation, the sediments of which were laid down during the Jurassic Period some 160 million years ago.

Much of present-day Colorado was then a flat, low-lying coastal plain with sandy beaches, marshes, and tidal flats at the edge of the warm, shallow Interior Seaway. A tropical climate and profuse vegetation supported a booming population of both herbivorous and carnivorous dinosaurs. Varying sea levels, periodic flooding, and heavy sedimentation combined to quickly bury dinosaur remains in an excellent environment for fossilization.

In relatively recent geologic time, erosion exposed sections of the fossil-rich Morrison Formation. In western Colorado, the Colorado River cut deeply into the sediments to carve out the sprawling Grand Valley, the present site of Grand Junction and Fruita.

More Than Meets the Eye

In some areas, huge, intact, fossilized dinosaur bones protruded from hillsides in plain view. Native Americans flaked the abundant, well-silicified dinosaur bone into tools and points. By 1885, ranchers and sheepherders near Fruita had begun collecting “big bones” to sell as curios to railroad travelers or museums in the East. Several even made bone-hunting a full-time occupation.

But the true significance of Fruita’s profusion of dinosaur fossils went unrecognized until the arrival of a 31-year-old paleontologist named Elmer S. Riggs in 1900. Riggs had studied paleontology at the University of Kansas. By the 1890s, he was an assistant paleontologist at Chicago’s Field Columbian Museum (now The Field Museum) and participated in field expeditions to Wyoming and South Dakota.

After assisting in several major dinosaur-fossil recoveries, Riggs became determined to discover a new fossil field of his own. But rather than just randomly searching, he began instead by writing letters to a dozen communities near Morrison Formation exposures in Colorado and Wyoming, asking if residents knew of any fossilized-bone deposits.

Among those who replied was Dr. S. M. Bradbury, a Grand Junction dentist and president of the Western Colorado Academy of Science. Bradbury reported that dinosaur bones were common near Fruita and that their deposits had never been scientifically investigated.

Intrigued by Bradbury’s letter, Riggs asked The Field Museum to fund an expedition to western Colorado. Hesitant to risk funds on unproven bone fields, the museum directors offered only limited support—if Riggs himself would pay part of the expenses.

Countless Discoveries

Riggs agreed, and in May 1900, a group of residents welcomed him at the

Grand Junction railroad station. Eager to show off their discoveries, they took him on a tour of known fossil sites. Within days, Riggs recovered the fossilized shoulder bones and vertebrae of the large sauropod Camarasaurus.

His first major discovery came only weeks later southeast of Fruita on a low rocky hill that now bears his name—Riggs Hill, where he excavated the nearly complete skeleton of a Brachiosaurus, a huge sauropod new to science. Riggs’ Brachiosaurus, 30 feet tall and 80 feet from nose to tail, was then the largest dinosaur ever found. (An articulated, cast-replica mount of this specimen is displayed today at Chicago’s O’Hare International Airport.)

Impressed with Riggs’ initial finds, the museum directors approved a return expedition the following year. They increased Riggs funding to $800, still very little for five months of equipping, feeding, and paying excavation crews, then transporting heavy dinosaur fossils by wagon and river raft to railroad freight depots for shipment to Chicago.

But this return expedition nearly ended before it began when a supply raft capsized, dumping its entire load of food and a ton of dry plaster (for encasing fossilized bones) into the Colorado River. Riggs considered calling off the expedition, but his local friends and supporters, including several serious amateur paleontologists, took up a collection to replace the lost food and plaster. During the following months, Riggs repaid their generosity with free lectures on fossil excavation and preservation and other paleontological topics.

In 1901, Riggs recovered the rear two-thirds of a Brontosaurus (later Apatosaurus) from a site just south of Fruita, now known as Dinosaur Hill. Quarrying the deeply buried bones of this 70-foot-long sauropod from a steep hillside was no easy task. When removing the huge volume of overburden on the steep hillside became impossible, Riggs was not discouraged: He simply hired hardrock miners to tunnel into the hill to recover the bones from the world’s first and only underground “dinosaur mine.”

Giving Birth to Dinosaur Paleopathology

Riggs’ Apatosaurus skeleton included several ribs that had been broken, but then healed during the dinosaur’s lifetime—a discovery that pioneered the specialized field now known as dinosaur paleopathology.

By September, Riggs had collected six tons of plaster-encased dinosaur bones to ship to Chicago—but couldn’t pay the freight costs. This time his friends persuaded the Denver & Rio Grande Western Railroad to help out. The railroad shipped the bones free of charge as a gesture to the advancement of science. Several years later, when The Field Museum displayed the spectacular, full skeletal mounts of Riggs’ recoveries, Fruita gained international recognition as one of the world’s leading sources of Jurassic dinosaur fossils.

Riggs’ last year of field work at Fruita was 1903, but his local legacy lived on. In the 1920s, local amateur paleontologists who had learned from Riggs began making their own fossil recoveries. The discoveries of Al Look and Ed Faber attracted scientific interest from several western universities. Then, in 1937, when local fossil collector Ed Hansen found in situ vertebrae above Riggs’ original quarry at Riggs Hill, another local amateur paleontologist, high-school geology teacher Edward Holt, excavated nearly complete, fossilized skeletons of Stegosaurus, Allosaurus, and Brachiosaurus.

In 1937, Al Look, astutely foreseeing the potential of dinosaur paleontology to future area tourism, suggested preserving Riggs’ original bone quarries. The first step came the following year with well-attended dedication ceremonies at Riggs and Dinosaur hills. The guest of honor was none other than Elmer Riggs himself, then The Field Museum’s curator of paleontology and one of the world’s leading paleontologists.

Another local amateur paleontologist was Grand Junction attorney Ivan Kladder who, during the 1940s, excavated and amassed an extensive, well-cataloged collection of dinosaur fossils.   

Museum Tends to It Origins

Elmer Riggs died in 1963, the same year that the Museum of Western Colorado was established in Grand Junction with dinosaur paleontology as its initial focus. Local amateur paleontologists provided the museum’s first fossil exhibits, including the entire Kladder collection.

Today, the Museum of Western Colorado, while greatly broadening the scope of its exhibits, has not forgotten its paleontological origins. In 2001, the museum opened a new exhibit facility in Fruita named Dinosaur Journey. Only two miles from historic Dinosaur Hill, it is dedicated entirely to dinosaurs and related aspects of paleontology and geology. Near the museum’s entrance stand colorful, near-life-sized models of a platy-spined Stegosaurus and a Ceratosaurus, the latter another tribute to Fruita’s official “town dinosaur.”

Interior galleries display the articulated casts of an 18-foot long Brachiosaurus forearm alongside photographic murals of Elmer Riggs and his crews at work in 1900. The largest of Dinosaur Journey’s eight full-skeletal mounts is a 50-foot-long Camarasaurus; the smallest is the predator Othnielosaurus, measuring just six feet from its nose to the tip of its slender tail.

Taking A Dino Journey

Dinosaur Journey also displays robotic dinosaurs that move, roar, and scream. These quarter-, half-, and life-sized models include such familiar genera as Tyrannosaurus, Stegosaurus, Triceratops, and Apatosaurus. Their realistic exteriors conceal interior aluminum frames, electric motors, and cam-operated shafts that impart motion to jaws, necks, forearms, and tails. A particularly dramatic model depicts Utahraptor, an 8-foot-tall, 20-foot-long “super-slasher” predator devouring the neck of a sauropod.

The roars and screams that echo throughout the museum are not random conceptions of dinosaur sounds. Drawing upon modern comparative anatomy and known dinosaur jawbone and neck-bone structures, paleontologists have modeled dinosaur vocal cords. The robotic dinosaurs’ roars and shrieks, specific to particular dinosaur genera, are based on sounds that actual dinosaur vocal cords would likely have made.

Locally recovered fossils are prepared for study and display in Dinosaur Journey’s working paleontological laboratory. The lab is staffed by professional paleontologists and volunteers who, time permitting, provide guided museum tours. Viewing windows enable the public to observe laboratory technicians working on locally recovered fossils.

One of the museum’s geology-related displays is fittingly called “Earthquake!!!” When visitors step onto a special floor section and press a button, they experience the simulated, but frighteningly strong, earth movements that would accompany a 5.3-magnitude temblor.

Making the Most of the Trip

Dinosaur Journey also distributes brochures and maps for the nearby field attractions—Dinosaur Hill, Riggs Hill, the Fruita Paleontological Area, and the Trail through Time. Dinosaur Hill, a few minutes south of Dinosaur Journey on Colorado Route 340, has a one-mile-long loop trail with interpretive signs. The hill’s summit offers panoramic views of Fruita, the Colorado River, the Grand Valley, and the canyons and spires of nearby Colorado National Monument. The trail passes the portal of the historic underground “dinosaur mine,” where a bronze plaque commemorates Elmer Riggs’ fossil recoveries 118 years ago.

In 1991, paleontologists reopened this underground mine where Riggs had recovered his Apatosaurus specimen—and recovered three Apatosaurus tail vertebrae that Riggs had missed.

Just a few miles from Dinosaur Hill is the Fruita Paleontological Area, 360 acres of deeply eroded badlands where fossils represent a greater diversity of Jurassic life than any other known place on Earth. Quarries here have yielded skeletons of such plant-eating giants as Apatosaurus, Camarasaurus, and Stegosaurus; the carnivore Ceratasaurus, and the two very small dinosaurs Echinodon and Fruitadens. A half-mile-long loop trail, marked by 20 detailed, illustrated, geological and paleontological interpretive signs, passes two historic dinosaur quarries, a dinosaur-track site, and a dinosaur-eggshell dig.

The Fruita Paleontological Area is also home to brightly colored collared lizards, some nearly a foot long. Males have blue-green spots and stripes, yellow-brown heads, sunflower-yellow forefeet and eyelids, and black collars. Although not descended from dinosaurs, collared lizards have a decidedly prehistoric look that adds to the interest of this paleontological area.

Riggs Hill, seven miles east of Fruita, has a three-quarter mile-long trail with interpretive signage that passes Riggs’ original Brachiosaurus quarry, now marked with a commemorative bronze plaque.

Modern-Day Discoveries

Fossil discoveries and excavations in the Fruita area continue today. In 1981, paleontologists Pete Mygatt and John Moore discovered an extraordinarily rich fossil deposit in Rabbit Valley 17 miles west of Fruita at Exit 2 on I-70. Today, this deposit is the Mygatt-Moore Quarry, a part of the Rabbit Valley Natural Research Area, which is jointly managed by the Museum of Western Colorado and the Bureau of Land Management. The quarry’s 1.5-mile-long Trail through Time features 21 interpretive geological and paleontological signs, and places where visitors can touch in situ fossilized dinosaur bones.

In late Jurassic time, Rabbit Valley was a silty watering hole where periodic

flooding created the conditions necessary for bone fossilization. The Mygatt-Moore Quarry has yielded more than 3,000 dinosaur bones, among them the nearly complete skeletons of the herbivores Apatosaurus and Camarasaurus, the carnivore Allosaurus, and the recently discovered armored herbivore Mymoorapelta (named after the quarry).

Just five miles south of Fruita, Colorado National Monument offers fascinating perspectives on the region’s dramatic geology. The rock exposures in this 36-square-mile tract of sheer-walled canyons, towering monoliths, and red sandstone cliffs represent a billion years of geologic time from the late Precambrian to the early Cenozoic eras. Views to the north and east across the Grand Valley and the Colorado River reveal the enormous extent of the erosion that exposed Fruita’s treasure trove of fossilized dinosaur bones.

Popular half-day, one-day, and five-day fossil digs at the Mygatt-Moore Quarry are open to the public on a fee basis. Scheduled by Dinosaur Journey throughout the summer months, these digs include transportation from the museum to the quarry, lunch, a special tour of the museum’s fossil-preparation laboratory, and hands-on, excavation work with instruction from professional paleontologists.

For a change of pace from the many paleontological attractions, visitors should consider the Two Rivers Winery on Colorado Route 340. Just a few miles from Riggs Hill and in the shadow of Colorado National Monument’s red cliffs, the Two Rivers tasting room offers an outstanding selection of varietal wines produced from locally grown grapes. It’s a fine place to contemplate the rich paleontological heritage of Fruita’s “Jurassic Park.”

Fruita is located just off Interstate 70 at Exit 19, 10 miles west of Grand Junction, and 19 miles east of the Utah line. Dinosaur Journey is a half-mile south of Fruita on aptly named Jurassic Court. The museum is open daily; hours vary seasonally. For further information, contact Dinosaur Journey at 970-858-7282 or visit www.dinosaurjourney.org.

The post Fruita: The Real “Jurassic Park” first appeared on Rock & Gem Magazine.

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The post Issue Highlights: February 2020 first appeared on Rock & Gem Magazine.

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The post Issue Highlights: December 2019 first appeared on Rock & Gem Magazine.