Opal is a well-known example of a mineral whose color is caused by a physical phenomenon called “diffraction.” Other phenomena include iridescence, a rainbow effect seen in iris quartz and pearls; chatoyancy, which we see in cat’s-eye stones and some malachite; asterism, which is displayed in star stones; aventurescence, as seen in aventurine quartz and sunstones; adularescence, seen in moonstone; and play of color, or the alexandrite effect, seen in the alexandrite variety of chrysoberyl and some garnets. In every one of these groups, the cause of the color is related to some internal physical structure and not a metallic impurity or element in the mineral’s structure.

Opal Color

For centuries, people tried to explain the play of color seen in many opals. Finally, in the 1960s, we developed equipment that could actually see the internal structure of opal. It revealed a very orderly arrangement of submicroscopic spherules of silica. These spherules and the spaces between them acted as a diffraction grating, spreading light into its various colors. The sizes of these spherules and the angle the light struck them, coupled with the viewer’s angle, determined which color wavelengths were canceled and which ones were reflected. Diffraction of light results in opal’s play of color.

Labradorite Color

A more common mineral that gets its play of color from diffraction is the feldspar mineral labradorite. This mineral can develop in huge formations, resulting in outcrops that give off flashes of color.

Labradorite crystallizes in thin wafers in parallel layers that repeat to form a diffraction grating. This has the effect of separating light into its colors, giving labradorite a play of color that depends, in part, on the angle of the source of light. The thickness of each crystal and each cluster of crystals in their parallel layers also affect which color is seen. Labradorite can flash bronze, blue, green, and in some cases, red or violet in an overall groundmass of gray to blue. It is thought the gray color of the groundmass is due to the scattering of light by the internal structure.

Play of Color

Another attractive feldspar mineral is adularia. Like labradorite, it develops as thin crystals that line up in parallel arrangement and act as a diffraction grating. But adularia does not show a play of color. The twinned arrangement of the crystals simply scatters light. While it can also be shades of gray, pink, peach, green and brown, it is best known for a bluish-white color that is reminiscent of the moon.

Properly cut adularia gives off a cloudy sheen that seems to float throughout the polished stone. We give this lovely form of adularia the name “moonstone.”

Why does adularia have little color, while labradorite is a riot of color? Minerals color variations are because of minor variations in the refractive index of the labradorite crystals involved. In adularia, the refractive indices of the crystals are virtually the same.

Iridescence

Iridescence is described as a play of changing colors on a surface of a mineral. A prime example is the look of oil spread over the surface of water. The oil particles have a different refractive index than the water, and this physical difference results in a play of color.

The most common example of this phenomenon is called “peacock ore”, which is actually the mineral bornite (copper sulfide). A freshly broken surface of bornite quickly oxidizes, forming a thin oxide mineral layer whose refractive index differs from bornite’s and creates a play of color. More subdued examples of this iridescence are seen on some crystal surfaces of pyrite, cuprite, chalcopyrite and hematite.

Pearl Iridescence

Iridescence is what gives pearls their soft, moonlike luster, called “orient.” Pearls are made up of layer upon layer of microscopic crystals of hexagonal aragonite. The refractive indexes of these layers are the same. Colored and black pearls result from inclusions that get into the pearl’s structure.

Mother of Pearl’s lovely shimmer, or glow, comes from the interior lining of shells, which is made up of two different substances: the calcium carbonate mineral aragonite, which forms microscopic hexagonal crystals, and conchiolin, a fibrous protein that forms in layers in parallel arrangement. The parallel fibers of the conchiolin are the key to creating the iridescence we see in mother of pearl, also called “nacre.”

Chatoyancy

When the fibers of a mineral develop in a parallel arrangement, they impart a silky shimmer or glow of light, called chatoyancy, that can be very appealing. You can expect to see this shimmer in a range of minerals. Asbestos is a very common example. When the asbestos is invaded by silica, it can form what we normally call tiger’s-eye, which is a very useful chatoyant gemstone with a silky luster. The invading silica negates the hazard we normally associate with asbestos.

Iridescence Within Stain Spar

One variety of gypsum, called stain spar, also shows iridescence, or glimmer of light. The mineral looks like silk cloth, whose fibers are also arranged in a tightly woven, parallel structure. Another example of iridescence is seen in some malachite. This copper carbonate usually crystallizes in tightly packed needles, which grow in slightly diverging radiating masses. When freshly broken, these near-parallel fibers give off a shimmering green color.

Asterism is seen in minerals like diopside, gem corundum, some moonstones, and several others. In these species, included fibrous crystals of the mineral rutile, in an intersecting arrangement, reflect light in a six-rayed star pattern. This physical phenomenon is what creates rare star sapphires and rubies, which are very valuable varieties.

Cat’s-eye gems exhibit chatoyancy, as well as a single, bright, linear reflection from tightly packed parallel fibers of a second mineral. Lapidaries give these gemstones a slight to strong dome and orient them so that the included mineral, often rutile or tourmaline, runs straight across the curved surface to form a single bright line, much like the vertical iris in a cat’s eye. It is important to know that these included needle crystals are all oriented along just one of the several growth axes of the hexagonal corundum stone.

Hexagonal Minerals

Hexagonal minerals like ruby and sapphire develop along four axes: one vertical “C” axis, from which three axes develop at right angles to the “C” axis, 60º from each other. For a star gem to form, the included mineral orients along the two arms of each horizontal axis to create a six-rayed star.

Chatoyancy is also seen in the cubic mineral gem garnet. The difference is that garnets form in the cubic system so the “star” forms from needle crystals that have oriented along the two horizontal axes that make up the cube form. Only two axes extend away from the single vertical axis, so the four arms of these axes with their parallel, included needles can orient to form a four-rayed star.

Understanding Aventurescence

Aventurescence is another physical phenomenon that involves inclusions. In this case, the inclusions are usually large enough to be visible and are scattered throughout the crystal mass, rather than oriented in a particular alignment. These scattered inclusions act as reflectors that scatter the light entering the host mineral.

An intriguing example of this is the manmade material called “goldstone”, which is glass with copper inclusions that give the glass a bright reddish-gold color.

Aventurescence is named for a quartz variety called aventurine, which is a lovely green color thanks to included chrome mica. These tiny, green flakes, or spangles, are scattered throughout the quartz, giving it a diffused green color of varying intensity that is very attractive.

The most attractive gem that falls into this category is the feldspar variety sunstone. This very lovely gem is found in several places in Oregon and shows a fine orange to red color due to included copper diffused throughout the gem. In some examples, the copper orients within the feldspar so that wisps and feathers of color are prominent in the gem. Sunstone claims in Oregon are occasionally opened to collectors for a fee.

Alexandrite Effect

Finally, the alexandrite effect is seen in very few minerals whose color is based on the type of light source. The chrysoberyl variety alexandrite is the obvious example.

Alexandrite has a light absorption band that, in sunlight, can split light into two different transmission areas. Under sunlight and fluorescent light, some of the blue wavelengths are absorbed, so green becomes dominant. When seen under in incandescent light, alexandrite is red.

As you collect colorful minerals, be aware that not all of them owe their color to a trace element inclusion. This is another area of interest you can pursue as you enjoy our wonderful hobby.

This story about what gives minerals color appeared in Rock & Gem magazine. Click here to subscribe. Story by Bob Jones.

The post What Gives Minerals Color? first appeared on Rock & Gem Magazine.

This is the first in a three-part series also covering types of gemstones with the letters J to R and types of gemstones with the letters S to Z.

What is a Gemstone? The definition of a gemstone isn’t quite as precise as the faceted beauties it describes. In general, when minerals, and sometimes organic materials such as amber, are cut and polished to create jewelry, we call them gemstones. There are nuances and outliers because some types of gemstones are too delicate to be worn, but most people in the gem world accept this general concept. To further clarify, types of gemstones are divided into “precious and semi-precious” stones with only diamonds, emeralds, sapphires and rubies encompassing the precious category. Everything else falls into the semi-precious zone, although this doesn’t necessarily imply inherent modern value or desirable characteristics. Regardless of the classification, there’s no question that when we can bring out the inherent beauty within these stones, it is something to be truly prized.

Agate

Agate is a silica-based mineral and is a popular semiprecious stone because of its attractive coloration and banding. Reportedly discovered by Greek philosopher Theophrastus roughly 2500 years ago, early people throughout the Middle East, Russia, and Greece used agates to create ornaments. According to research by the Bureau of American Ethnology, Indigenous People utilized them in much the same way.

Agate is a chalcedony, which is a type of cryptocrystalline quartz. Like many stones in this category, it’s created when groundwater seeps into the igneous rock where silica deposits form concentric layers within the rock cavities and crevices to create the telltale banded patterns.

The wide variety of colors, ranging from brown, black, white, red, gray, pink and yellow, are because of impurities in the groundwater. With a seven on the Mohs rating, agates are on the upper end of the hardness scale. This makes this translucent stone a favorite for rock tumbling. It’s often used for jewelry as well.

Bloodstone

An opaque, dark green type of gemstone, bloodstone features distinctive orange to scarlet red splatters that look like blood at first glance. This is the telltale signature of this traditional birthstone for March. The more modern birthstone choice is aquamarine.

Bloodstone is also called heliotrope, a name derived from the Greek helio meaning sun and tropos meaning toward the sun. If you garden, you’re familiar with heliotrope plants that turn toward the sun as they grow. This name indicates how the stone reflects the light. Along with legends of healing powers, bloodstone is also known as a protective stone. People will often wear or carry bloodstones to keep threats at bay.

The minerals chlorite and amphibole are responsible for the deep green coloration while iron oxide inclusions create the blood-red speckling.

Carnelian

Carnelian is one of the least expensive chalcedonies, the translucent yellow-orange to rich amber or even reddish-brown gems darken when heat treated. This includes the heat of the sun, so it’s best to keep your stone out of the sun to keep the color true. Iron is responsible for the red coloration and it’s what oxidizes and deepens when exposed to heat.

Carnelian is sometimes confused with jasper, although jasper is a type of gemstone that is typically a deep red and is opaque, rather than translucent. Plus, jasper often exhibits banding patterns on its surface appearance.

Carnelian is found throughout the world with some of the highest quality stones found in Scotland, Brazil and Washington State.

Even though it’s relatively inexpensive, many so-called carnelians are dyed and heat-treated agates. To determine if a carnelian is real, hold it up to the light. If it’s a natural carnelian, it looks cloudy. If it’s a heat-treated agate, it will most likely show striping.

Dumortierite

Although colors range from brown, green, and the rarer violet and pink, the eye-catching denim blue of this type of gemstone is probably the most popular with gemstone enthusiasts.

An aluminum boro-silicate mineral, dumortierite occurs in regions of high metamorphic activity that are also rich in aluminum and boron. Manganese, iron, and sometimes zinc inclusions, are responsible for the blue coloration.

Dumortierite was first described in 1881 after being found in the French Alps. It was named for the French paleontologist, Eugene Dumortier.

Dumortierite has a glassy (vitreous) luster. Its fibrous nature creates fine, almost hair-like radial crystals within the structure. The blue variation is sometimes mistaken for lapis lazuli, but dumortierite is typically a deeper blue or violet, plus lapis lazuli sports white or gold metallic flecks because of the pyrite within it.

Dumortierite quartz is quartz with inclusions of dumortierite.

Emerald

The birthstone for May, emeralds are a type of gemstone that earns their place as an adjective to describe a particularly intense green. The name is derived from the Greek word smaragdos, meaning green stone.

Created in metamorphic rocks when hot magma flowed over and through the crevices of limestone and shale, emeralds are a beryllium aluminum silicate. Although emeralds are a type of beryl, not all beryls are emeralds. While green beryl is still green, it’s distinctly lighter.

Chromium oxide is responsible for the emerald’s deep green. Other gems, such as peridot and tsavorite garnets, are also found in green hues but not with the same vibrancy. Registering 7-8.5 on the Mohs hardness scale and forming in hexagonal crystals, emeralds are long favorites for precious jewelry, but fakes abound. To determine authenticity, inspect the stone with a 10X loop. Flaws and inclusions, particularly a small crystal within the stone, indicate a natural emerald. Air bubbles or even a “too perfect” stone are tell-tale signs that it is not real.

Fluorite

Made of calcium fluoride, pure fluorite is colorless, yet samples are commonly found in shades of purple, golden-yellow, green, blue, pink and brown. These types of gemstones are translucent to nearly transparent with attractive banding. The term “fluorescence” became part of the terminology when physicist Sir George Gabriel Stokes was working with fluorite in 1852. Although fluorescence doesn’t consistently occur, fluorite is known to glow when there is the presence of uranium, yttrium and other rare earth elements. It often emits blue, although yellow, green, white and red shades are possible.

Also called fluorspar, it’s been produced in Illinois since the 1800s and is the state mineral. Often forming in cubic crystals, it is popular for jewelry but has a wide number of commercial applications ranging from an ingredient in ceramics to a flux used in refining metals.

Garnet

Many people picture garnets as red stones, but these types of gemstones are also found in shades of orange, pinkish-orange, green, reddish-purple, colorless and even blue and green, albeit these last two are rarer.

Garnets are formed when aluminum-laden sedimentary rock is metamorphosed. Garnets are one of the most widespread types of gemstones throughout the world. While the bulk of garnets is mined for industrial applications, it’s one of the oldest known gemstones and has been used for ornamental purposes for 5000 years. Historical evidence shows stones within the necklaces of pharaohs. Garnet signet rings were used by Roman leaders to seal documents.

Sometimes mistaken for a ruby, garnets are usually a darker red with brownish tones. When it’s held up to the light, yellow bands are often visible in a garnet while a ruby will be clear.

Hematite

Consisting of 70 percent iron, hematite is one of the primary ores of iron. Fortunately, it is one of the most abundant minerals on Earth. According to NASA, it’s also the most abundant mineral on Mars. The iron-rich environment is why Mars is dubbed the “red planet.”

Named as far back as 300-325 BCE, hematite is derived from the Greek haima, meaning blood. These types of gemstones are found in colors ranging from rust-red, brown, steel-gray to black, it always leaves a red streak when scratched on a scratchpad.

The distinct reddish hue has been used in artwork from the earliest cave paintings. It was a key pigment for Renaissance artists creating paintings with canvas and oil in the Middle Ages. Besides its importance as an ore for iron and in art, it effectively stops radiation making it useful in shielding applications. Plus, it creates a beautiful tumbled stone for those who love to collect them.

Iolite

This beautiful violet-blue stone was the secret to the Vikings’ success in crossing the ocean as they looked through a thin iolite specimen to determine the position of the sun on cloudy days. The key to this unique quality is called pleochroism where different colors are visible at different angles. For example, a piece of iolite may have the classic violet-blue hue on one side, but when it’s turned over, it appears yellow or clear.

A silicate of aluminum, iron and magnesium, iolite (also known as the mineral cordierite) is created in metamorphic and igneous rock formations. Derived from the Greek word ios meaning violet, some iolite is blue enough to look like a sapphire. Some speculate this quality is because of the presence of titanium, although iolites are easily distinguishable because of pleochroism.

This story about types of gemstones appeared in Rock & Gem magazine. Click here to subscribe. Story by Amy Grisak.

The post Types of Gemstones By Letter (A-I) first appeared on Rock & Gem Magazine.

Starting a Rock Store

Isobel Medley was an only child and was raised in the early 1920s on a prairie farm in Carberry, Manitoba. She attended a one-room school with one teacher for first through 12th-grade students. Isobel developed a strong interest in rocks and geology in those formative years. She eventually moved to Vancouver, British Columbia. In 1945 she married Al, for whom she waited eight years for his return from the War. She became the mother of three children while studying geology. Her love of rocks ultimately inspired her to open a rock store.

The Fraser Rock Shop opened in 1960 and it became the place her daughter Velma spent most of her childhood every day after school. Velma holds many fond memories of her experiences there. For instance, the original shop was located next to a Chinese market – one that Velma frequented when the fresh produce was being delivered. She remembers the shop had an apartment upstairs and she often played with children who lived there.

Quickly though, the shop grew and needed more space. Isobel had visions of a larger shop and space to teach classes. Velma recalls that this move, also on Fraser Street, brought the shop closer to her middle and high school. Growing up in a rock shop, Velma developed skills that helped her throughout her life – listening, providing for each customer, public speaking, asking questions and developing relationships that lead to lasting clients. In those years, Velma didn’t realize just what a skilled lapidary her mother was.

Isobel was a lifelong learner and pursued lapidary skills that reflected her expertise and experience, and Velma learned those same skills.

A Family Affair

The Fraser Rock Shop may have been Isobel’s brainchild, but it was really a family affair. Velma recalls her father Al being an active part of shop operations. He was a career business agent and traveled during the week, but on weekends he was involved in cutting larger rocks — Brazilian agates, jades and petrified woods to name a few. Eventually, their mutual interest led Al to purchase a jade mine with a partner. Helicopters were needed to fly to the Birkenhead Jade Mine in the interior of British Columbia where huge, on-site saws were used by her father to cut pieces of jade which were later sold in the rock store.

Velma recalls that family vacations included spending time rock hunting. “It didn’t matter what direction we were traveling; we were always looking for rocks,” Velma explained. She still has a jar of opals she collected in Mexico on a family adventure. Trips also provided insights into how stonework was done in other parts of the world. For example, Velma remembers antiquated tools in use in Mexico and a stunning European trip where they observed rocks being cut by lapidary artists lying on their stomachs.

Rock Store Adventures

Growing up in the rock shop seemed natural to Velma. She didn’t realize how uniquely special it was until high school. Velma had many wonderful experiences working alongside her mom. For instance, she recalls her mom announcing her participation in a local children’s television program called “Show and Tell.” Her mom thought it would be a great experience for her and suggested she speak about thunder eggs.

Thundereggs are found in Oregon and are formed in rhyolite lava. Customers to the shop found them to be interesting – and would choose one to cut with a diamond blade saw to reveal their internal patterns and colors. “I was feeling mortified, scared and nervous,” Velma said. “Mom stayed focused on the positives and I being obedient and not wanting to let her down, agreed to participate.” While Velma doesn’t remember the filming beyond the gentleman who took her through it, the experience was an opportunity to learn and grow.

Another time Velma recalled waiting on a young, handsome man with curly blond hair. He wanted to have a special pendant made for his fiancé at the time. Her mother cut and polished the stone, setting it to his preselected settings. Later they learned that this young man was the Canadian musician Terry Jacks, famous for the song Seasons in the Sun.

Developing Clients

Slowly, Velma developed clients of her own. She worked for a visually impaired gentleman who paid her to polish the stones he would give as gifts. Velma’s mother tasked her with teaching a legally blind girl to shape cabochons on the grinder. This was a good challenge because it’s easy for a sighted person to grind away a layer or two of skin!

“There was a lot of activity in the rock shop, so it was fun being there,” Velma said. Not only were there classes for adults and youth, but often people came in and rented equipment by the hour. People renting equipment for .35 cents an hour always had her mom as a resource while polishing and cutting stones. The shop was a hub for rock club events, students of all ages and anyone interested in learning about rocks.

Lifetime Achievements

“I do admire the sense of achievement my parents shared throughout their lives,” Velma declared. “The joy of work for us, I think, could be attributed to all the wonderful people we met, helped, taught and encouraged.”

Velma went on to say that over the years, they had belonged to a couple of different rock clubs building life-long friendships that spanned fun annual gatherings, food, games, music and memories which of course included attending rock shows!

“Rockhounds come in all ages,” she added. “Even from prairie farms.”

Rocks for Sale

While Velma was living in Alberta, her parents sold the rock store in the mid-1980s, (or so she thought) only to fully realize after their deaths that they had retained their extensive collection of finished jewelry, cut and uncut stones. Recently, Velma has been working to sell the entire collection.

This story about growing up in a rock store appeared in Rock & Gem magazine. Click here to subscribe. Story by Deb Brandt.

The post Growing Up in a Rock Store first appeared on Rock & Gem Magazine.

After 30 years of procrastination, I purchased a brand-new rock saw and grinder/polisher. Wow, did I have fun! For that first few months of cutting and grinding, I was in seventh heaven. All those lovely rocks I had lusted after for so long were finally put under my polishing wheel: lapis, agate, jasper, tiger’s eye, malachite, turquoise, chrysocolla and quartz.

But I soon began to experience a nasty and completely unexpected cavalcade of health problems: coughing, hoarseness, difficulty clearing my throat, breathlessness, and a dull ache in the pit of my lungs. Of course, I had always worn safety glasses with side protection, as recommended in every manual, but a mask seemed a cumbersome hindrance. As the situation worsened, I tried several dust masks, but there was little improvement. It was time to do a little research, so I hit the books and started talking to fellow rockhounds. It was a revelation. Rock dust from lapidary work turns out to be more than just a nuisance; it can be deadly.

Dangerous Dust

A single heavy dose can cause crippling lifelong problems. It attacks the lungs in a variety of ways: First, by coating the inner lining and blocking the transmission of oxygen into the bloodstream. Second, tiny sharp fragments slice and cut into the alveoli, which coat the inner lining of the lungs, causing irritation and inflammation. Fresh dust seems to be more harmful because the sharp edges have not had a chance to be softened by moisture. Some forms of rock dust are quite poisonous in and of themselves. Whether it is inhaled, ingested, or contacted by exposed skin, the effect can be injurious to your health.

Copper Oxide Minerals

Among the worst offenders are minerals containing copper (II) oxide (CuO), the higher oxide of copper, which can cause damage to the endocrine and central nervous systems. These minerals include some of our most colorful and treasured semiprecious stones: turquoise (9.8% copper oxide), chrysocolla (45%), and malachite and azurite (70%). These percentages are only close approximations; each rock has its own signature of impurities.

It is worth remembering that other closely related copper compounds are highly bioactive and have been used in pesticides, fungicides, and wood preservatives for decades. This is dangerous material. These high-copper rocks should not be licked to bring out the color, and oil mixed with the dust should be carefully cleaned off exposed skin.

Several lapidaries who smoke have described their own novel test for overexposure: Apparently, copper-impregnated dust combines with nicotine and tobacco tar in saliva to form a sickeningly sweet compound similar to saccharin. When their mouths start to taste like a candy factory, these rockhounds know it’s time to quit. Another sign is influenza-type symptoms. Symptoms of CuO dust poisoning mimic the flu, causing headaches, coughing, sweating, sore throat, nausea and fever. Skin, eye, and respiratory tract irritation are also common, along with a distinct “metallic” taste. A common name for these health effects is “metal fume fever.”

Silicate Minerals

Almost all the rocks most favored by cutters and polishers contain compounds that can be dangerous when inhaled. Silicates are the most common family of minerals on Earth, and silicosis has long been one of the chief hazards facing stonemasons.

The ancient Greeks and Romans were the first to observe its ravages and correctly associated the problem with mining and rockwork. Similar to the “black lung disease” of coal miners, it came to be known in later years as “grinder’s consumption.” The simple steps taken to prevent it were a major achievement in the modern field of occupational health. Ironically, although silicosis is well understood today, thousands still die from its effects every year, mainly from mining and sandblasting in the third world.

The symptoms of inhaling crystalline silica (SiO) dust include shortness of breath, cough, fever, emphysema, pulmonary fibrosis, lung scarring, and increased susceptibility to tuberculosis and cancer. Silicosis often takes many years to develop from repeated exposure to low doses of dust, but once established it is irreversible.

Widespread Silicates

The silicates include a bewildering variety of precious and semiprecious stones. In fact, it’s hard to imagine the world without them, as they can be found in every class of rock and occupy a niche in every conceivable geological environment on the planet.

The family includes quartz, chalcedony, jasper, agate, aventurine, bloodstone, carnelian, chrysoprase, amethyst, opal, onyx, beryl, petrified wood, obsidian, flint, chert, soapstone, sandstone, glass and tiger’s eye. In almost all of these, the content of silicon dioxide approaches or exceeds 50%.

It should be mentioned that African tiger’s eye also exposes the lapidary to another potent danger: asbestos. The vibrant optical effect of its chatoyancy is caused by parallel-oriented, finely fibrous amphibole asbestos. Serpentine has a high chrysotile asbestos content, but this is not considered quite as dangerous as the tiger’s eye. Some soapstone varieties also contain asbestos and should be cut or carved with caution.

Fossil Dangers

Radioactivity from fossils is a hazard that isn’t often top of mind. In a recent study of 300 randomly selected fossils from the Hagerman Fossil Beds of Idaho conducted by C. Neal Farmer, Ronald L. Kathren, and Craig Christensen, a handheld Geiger-Müller survey instrument detected discernible levels of radiation one to two orders of magnitude above the ambient level of background radiation in three-quarters of the specimens (“Radioactivity in Fossils at the Hagerman Fossil Beds National Monument”, Journal of Environmental Radioactivity, Vol. 99, Issue #8, August 2008, pp. 1355-1359). That is a huge difference.

In some areas, like the Hagerman Fossil Beds National Monument (Idaho) and the Morrison Formation at Dinosaur National Park (Colorado/Utah), fossils have even been hunted using Geiger counters.

According to the study, radioactive fossils seem to occur most commonly between 900 and 1,000 meters above sea level in ancient sandy riverbeds, while clay-rich deposits and those at other altitudes do not seem to show these high levels. Apparently, naturally occurring uranium produces radium, which decays into radon, an inert gas. Ancient groundwater transported these radioactive elements into sandy fossil-bearing areas, where they precipitated out of solution during the fossilization process. Even small fossils like shark teeth and trilobites can have significant readings.

The National Park Service is so concerned that it put out a “Conserve O Gram” with detailed instructions for handling and displaying specimens. While it is probably safe to collect most fossils, at the very least, you should wash up and change your clothes after leaving the field. And always wear a respirator when you cut or polish the pieces—radioactive dust is highly carcinogenic!

Tips for Safe Handling

But enough of the doom and gloom. A few simple precautions can almost completely eliminate the threat of injury from most rock dusts. Here is a list of suggestions that will make your workshop a lot safer and allow you to enjoy lapidary work in good health.

1. Wear a Mask

Always wear a National Institute for Occupational Safety and Health (NIOSH) approved respirator with replaceable cartridges and dust filters. Some cartridges today combine a prefilter with the cartridge, which makes things simpler.

Respirators provide a wide variety of protection against dusts, solvents, fumes and mists. They are designated N, R and P, depending on the cartridge’s ability to filter out oil; N stands for “no protection”, R for “resistant to oil”, and P for “oil-proof”. The number that follows the initial tells you what percentage of the particulates is filtered out by the cloth prefilter. For example, an N-95 respirator will not keep out oil spray but will screen out 95% of airborne dust particles.

Avoid cheap dust masks; they don’t fit tightly enough and they filter poorly. If you can, try on several different respirators at the store to get the best fit. Shave your beard, if you have one, to get an airtight seal. Store the mask in a closed container or plastic bag when it’s not in use, and occasionally wash it with warm soap and water, both inside and out.
Try this simple negative pressure test on your respirator: Block up the air inlets, breathe in, and hold your breath for 20 seconds. If the mask is still held airtight against your face, it fits. Cartridges should be changed after about eight hours of use.

2. Work Outside and/or Ventilate

An open window or air conditioner does not provide adequate ventilation for the lapidary workplace. The simplest solution is to work outside. This keeps most contaminants out of your workshop and costs nothing, but it is not always possible.

If inside is your preference, consider setting up a local exhaust ventilation system. This would include a dust hood to collect contaminants, ducts to carry them outside, and a suction fan to power the system. Adjustable blast gates would allow a dust hood to be placed next to each appliance. Ducts should be circular, with as few bends as possible, and should exit the shop. If you have close neighbors or are processing a lot of rock, provide a dust collector to remove contaminants from the vented air.

Setting up such an elaborate system can be expensive and time-consuming for the part-time hobbyist. Some woodworking tool suppliers have come up with an ingenious alternative. They have adapted a wet/dry-type vacuum cleaner with a High-Efficiency Particulate Absorbing or Arresting (HEPA) filter to collect shop dust using a little extra pipe and some suction nozzles. There is no reason this system should not work for rock dust, as well. The vacuum should be placed outside the house because the dust-laden air sucked into the intake will be blown out the vacuum’s exhaust port. Even HEPA filters fail or become clogged, and some dust will always slip through. It’s far better for it to be blasted outside than into the shop or another enclosed area. Kits, diagrams, pipe and suction nozzles are available on the internet. Search for “dust collection” and “dust collection network”.

3. Lubricate

Always use water or oil as a lubricant when cutting, drilling, polishing or faceting, but be aware there are problems with both fluids. When water evaporates, it stops holding the dust down, allowing it to become airborne. A fine oil mist laden with toxic dust can be kept out your lungs with a good respirator, but it will settle on skin surfaces and stick like glue. Also, most lapidary oils are highly irritating or downright poisonous to breathe. Some, like old-fashioned kerosene, are dangerously flammable, as well. Everyone has their favorite method, but I work outside using mineral oil and a P (oil-proof) respirator cartridge with a built-in 100% particulate filter.

4. Cover Up

Always wear a head covering and apron and/or coveralls when grinding, and change clothes after you have finished. Rock dust loves to stick to clothing and hair, and you will carry it around the house and breathe it all day long (as will your family) if you don’t change. Take a shower after your lapidary work, shampoo your hair and use lots of soap. Launder coveralls and work clothes frequently. Disposable clothing, coveralls, and an apron might also be an option.

5. Don’t Sweep

Never dry sweep the workshop. Most of the dust will just become airborne and migrate elsewhere. Use a vacuum cleaner with a HEPA filter instead. If you really want to get down and dirty, use a wet mop on the floor and a wet rag with a water bucket on other surfaces.

Not all of these suggestions need to be slavishly followed. If you grind infrequently, you can probably forget some of them, but if you are an addict like me, you might want to implement most. Individuals vary greatly in their tolerance to rock dust. Some will go through life with nary a problem, but others can be extremely sensitive. Low doses on a daily basis will slowly accumulate, and that dust isn’t going anywhere once you breathe it in. Smoking and living with a woodstove or in an area with poor air quality will make you that much more vulnerable to problems. Listen to your body. If your lungs start to complain, take more precautions; you only have one set to last a lifetime.

FURTHER READING: Health Hazards Manual for Artists, 6th Ed., by Michael McCann Ph.D. and Angela Babin (Lyons & Burford Publishers, 2008)

This story about how to handle lapidary minerals safely previously appeared in Rock & Gem magazine. Click here to subscribe. Story and photos by Douglas Hamilton.

The post 5 Tips to Handle Lapidary Minerals Safely first appeared on Rock & Gem Magazine.

In Montana, gold and silver drew those looking for wealth to these remote realms. In the 1860s, prospectors found a smattering of gold in the waterways, although silver quickly drew more attention. By the following decade, it was silver that launched the mining empire of future moguls, William A. Clark and Marcus Daly, who segued into copper as the silver market cooled.

With technological advancements in mining and smelting, copper gained momentum beginning in the early 1880s. A pivotal moment was when Daly visited a newly blasted shaft in the Anaconda Mine, and after examining the black rocks containing the copper ore chalcocite, he reportedly proclaimed that Butte would be “the richest hill on earth.”

His pronouncement became a reality. According to the Mining History Association, in 1896 Butte produced 26 percent of the world’s copper supply and 51 percent of the United States’ needs as one smelter alone produced two million pounds of copper every month.

An International Metropolis

Butte is currently home to around 35,000 people, however, Aubrey Jaap, the director of the Butte-Silver Bow Public Archives, says that “(Butte) really peaked before and during WWI.”

By 1917, the population reached 100,000 with approximately 450 mines in operation. Nearly unlimited work opportunities drew immigrants from throughout the world with the note-worthy saying, “Don’t stop in America, go straight to Butte!” There were so many ethnicities that no-smoking signs within the mines were typically displayed in 16 different languages.

Butte was ethnically diverse and bustling with energy. It was a cosmopolitan city when much of Montana was not much more than cow towns. With the abundance of drive and expertise, the architecture of the growing city reflected the ambitions of its residents. International cultures lead to world-class restaurants and active civic organizations. At its height, Butte was a city that never slept.

Hardscrabble Life

This prosperity came with a price as wealth was built on the backs of the miners and their families.

“It wasn’t an easy place to live,” said Jaap. “There were no trees because they needed timber for the mines and to feed the furnaces.” With the smoke and pollution from the continually churning smokestacks, it was the image of industrialization.

“There was noise in town all of the time,” said Jaap who noted residents were accustomed to the constant hum of commerce. “What was scary was when it stopped,” she said because this typically meant a tragedy in the mines.

Deepening Mine Shafts

Initially, mining began with a pick and shovel, with explosives expediting the process while evolving into utilizing a windlass for shallow depths, and then a whim where a horse walked around a pivot to hoist up men and materials. As the mining shafts deepened, headframes, many that still dot the landscape, stood up to 200 feet tall to transport ore and workers sometimes over 5000 feet deep.

It was another world working underground. Extreme conditions took their toll. Jaap noted in the early days the men would emerge from the hot conditions of the mine soaking wet from sweat, water used in dust abatement and natural water within the mine itself. During the winter, temperatures rarely climbed above freezing and often hovered around -40°F. When the men came out of the mine in wet clothing into the bitter cold, they often succumbed to sickness, including pneumonia. This was resolved in later years by a dry room where they could change into dry clothing at the end of their shift.

Men had to work in pairs as a rudimentary safety system. They typically worked 12-hour shifts. Before electricity, candles and oil lamps were used for light.

Initially, the men shoveled all of the material in the carts, and while a man could push a single cart once filled, a horse could pull up to five. Horses and mules spent years in the mines before their own poor health, or death, was their ticket to the upper world once again. This practice continued until pneumatic locomotives, and eventually, electricity supplied the power. The last horse was brought up from the Emma Mine in 1937.

A Dangerous Profession

There were lots of ways for injury or death in this profession. Besides the taxing working conditions, breathing stale air and dust caused a condition called silicosis or “miners consumption.” Constant exposure to heavy metals contributed to cancer and inflammatory diseases and accidents were common.

Working with explosives was also dangerous. After drilling holes, miners placed a stick of dynamite in each using a piece of wood to carefully push it into place. This is where the common phrase, “Tap ‘er light,” came into being. Fuses were grouped 12 to 15 in a bundle. Workers had roughly eight to 14 minutes to get away from the blast zone once it was lit.

Even equipment that was supposed to make life easier could be deadly. The mucking machine, which was brought on board to save the men from shoveling, could decapitate miners.

It’s estimated that over 2,000 men died in the mines.

North Butte Mining Disaster

On June 8, 1917, during the height of production with well over 14,000 men working around the clock to supply the copper needed for World War I, 410 men descended into the Speculator Mine for the night shift. A cable falling to the 2400-ft. level created a cascade of events that left 168 men dead.

Just before midnight, four men lowered into the shaft to retrieve the five-inch diameter electrical cable that was being installed to create a fire alarm system. What they didn’t realize was when the electrical cable fell it tore the protective lead exterior of another nearby cable, exposing the paraffin-coated paper used for insulation. When one of the worker’s carbide lamps accidentally touched the cable, it ignited immediately. The mine shaft became a “mighty geyser,” and the sound of the disaster woke residents. Flames and toxic smoke turned the levels into a smoke-filled maze, killing or trapping nearly half of the men.

Personal Stories

Quick thinking during the disaster saved lives. For example, Mannus Duggan, a 25-year-old nipper (a worker who sharpened and made sure the men had their tools), sealed himself and 25 others behind a bulkhead made of timbers and their own clothing, while J. D. Moore, a shift boss, did the same with seven others. Even though oxygen – and time – ran out for some of the men most of them in these situations survived. Duggan was among them, but he ultimately succumbed to the toxic gases when he returned to the shaft to look for lost companions.

Throughout the ordeal, both men wrote to their wives, including Duggan’s missive: By the time all the men were rounded together Friday night we were all caught in a trap. I suggested we must build a bulkhead. The gas was everywhere. We built a bulkhead and then a second for safety. We could hear rock falling and supposed it to be the rock in the 2400 skip chute. We have rapped on the air pipe continuously since 4 o’clock Saturday morning. No answer. Must be some fire. I realize the hard work ahead of the rescue men. Have not confided my fears to anyone, but welcome death with open arms, as it is the last act we all must pass through, and as it is but natural, it is God’s will. We should have no objection.

A Labor Dispute

The incident ignited a simmering labor dispute. Grievances against the Anaconda Copper Mining Company and conflict with the Industrial Workers of the World (IWW), a socialist organization that effectively crushed the unions several years prior, made the timing right for a fight. The Speculator Mine disaster was all it took to incite violence, including lynchings, resulting in calling in federal troops and the passage of the Montana Sedition Act, which clamped down on any speech or actions contrary to the war effort. In the end, workers received few benefits, while the unions never regained their full power.

From Underground to Open Pit Mines

After WWI, underground mining shifted to more expedient open-pit mining. Created in 1954 by the Anaconda Company, the now infamous Berkley Pit, absorbed entire suburbs as the company expanded the operation. When copper prices fell in the early 1980s, the new owner, Atlantic Richfield Company (ARCO) ceased operations. In 1983, they removed equipment and shut off the water pumps, creating the now 1000-foot-deep, highly toxic, lake.

Ironically, the same metal-laden, acidic water that eats metal flooded the world beneath the town and provides an unusual benefit. Jaap said, “Actually, the water preserves (the timbers), but it makes (the mine shafts) inaccessible.”

The Berkley Pit is now a Superfund Site and a must-see point of interest in Butte, but mining still is the heart of the town. Jaap said the Continental Pit, the former location of Columbia Gardens that once provided a green respite for Butte families, is where silver, zinc, and copper are mined.

A lot of things we do today have a cost,” said Jaap. “For Butte, it’s really visible.”

Residents are proud of their heritage of bringing these important minerals to the world. “The Butte people and their families worked really hard and they take pride in it,” said Jaap. And well they should.

This story about the Butte, Montana, previously appeared in Rock & Gem magazine. Click here to subscribe. Story by Amy Grisak. Photos courtesy of the Butte-Silver Bow Archives.

The post Butte, Montana: Copper Mining first appeared on Rock & Gem Magazine.

For instance, the Finger Lakes region of central New York is known as “wine country” but one of its unexpected collectibles is the lake beach glass, sometimes still faintly bearing the etched lettering of its origin story, found with particular prevalence along the eastern side of Seneca Lake at Lodi Point Beach State Park.

Why? Old wine bottles: Castaways of vineyards past.

But rarer still are the ancient maritime castaways of ale and rum bottles from the Golden Age of Piracy (1650-1730), known as “pirate glass,” that wash up on the beaches along the Caribbean, North American eastern seaboard, West African, and Indian Ocean shipping lanes and trading ports.

Such Shanghai surprises tantalize collectors but not every dark piece tells the same story. Because, as Captain Jack Sparrow liked to say, “Not all treasure’s silver and gold, mate.”

Sea Glass Color – The Dark Side

Pirate glass is colloquially described as “black” but the intensity of what is more likely to be blue, brown, green, purple or red glass has been deepened by the addition of cobalt, copper or iron oxides; or during the glass-making process, the addition of iron slag, or coal and wood ash.

Why darken glass? To extend the life of products and their transport because darker glass protects valuable liquids (like alcohol or oil) from degeneration by sunlight.

The same properties added to deepen color also improve the structural integrity of the glass and make it less likely to break during handling and storage.

At sea, water may turn too contaminated to drink, but not ale or rum. Or a seafaring elixir of lime, sugar and rum often kept aboard in dark bottles as a survivalist measure against scurvy.

The strong, dark glass was perfect, beachcombing blogger Kirsti Scott notes, “For pirates on seafaring ships!”

Stones & Scallywags

Black joins gray, orange, teal, turquoise, red and yellow as the seven most difficult sea glass colors to discover. Pirate glass looks black but not all black glass is old enough to truly be “pirate.”

Well after the 17th-century heyday of pirate ships, early 19th-century decorative black glassware, known as Black Amethyst, was produced, as were black glass buttons to accent Victorian French fashion and, in more mundane industrial use, for light bulb insulators produced in plants like the General Electric and Vitrite Company in Ohio.

Slag Glass

Vitrite also happens to be the name of the slag glass often used as a dielectric, or electrical insulator, at the bottom of common light bulbs and consisting mainly of ground glass with “copious amounts of lead and manganese oxides, the latter being responsible for the dark purple color.”

In fact, Black Amethyst has become its own desirable sea glass collectible, with pieces more than 80 years old washing up along the Great Lakes and particularly Lake Erie, where these incandescent light bulb plants operated.

Still, other black beach glass pieces can be found downstream of defunct glassmaking factories, the remnants of bars or nuggets used to colorize clear glass. Also, blue-black glass traces to gin bottles from Holland, and red-black glass to Portugal.

While no less lovely to look at or bring home, these glass pieces lack the unique merits to claim provenance beneath the Jolly Roger.

Ahoy, Pirates

What helps qualify a piece of black sea glass as “pirate glass” is age (glass from the mid-17th century was hand blown) and location (albeit not all seafaring routes had to be Caribbean).

Pirate glass is noteworthy for its size, for the number of bubbles trapped inside its glass, and for its primitive density that (when held up to light) can reveal a “glow” along the edges of its true dark amber, olive green, or purple color. Older pieces may be so dense and opaque that light will not shine through them.

“Pirate ships were no strangers to the shores of the Outer Banks [of the Carolinas], and neither were their rum bottles. After hundreds of years of these bottles being tossed around by the sometimes extremely violent and vicious waters of Hatteras Island, these black chunks occasionally appear on the shore, to a beachcomber’s delight,” collector Kristin Hissong recounted in 2020 for the Island Free Press.

Knowing What to Look For

The trick is knowing what you’re looking for because pirate glass, by virtue of its dark color, blends almost too well into a beach’s natural background and can look a lot like any other average black stone.

“The first time I found a piece of pirate glass,” Kristin says, “I was going back and forth over one little shell bed gathering other treasures. When I first noticed the piece in the sand, I dismissed it as asphalt. It was about four inches long and looked like a black chunk of NC Highway 12.

“I didn’t know sea glass could be so big or so dark. But right before I decided to leave, I thought I might as well pick it up, and to my delight, it was a huge chunk of black sea glass.

“When I held it up to the light, it glowed a deep olive green and the glassmaker’s breath was caught in an air bubble inside the glass,” she noted.

“Ahoy matey, we found Pirate Glass!”

This story about sea glass color previously appeared in Rock & Gem magazine. Click here to subscribe. Story by L.A Sokolowski.

The post Black Pirate Sea Glass Color first appeared on Rock & Gem Magazine.

A Form of Coal

Coal is technically a rock, a combustible material formed by the decomposition and destructive distillation of biomass material in an oxygen-free environment. Coalification, the process of coal formation, begins when layers of plant material become buried and compressed under new forest growth and sediments. Elevated temperatures and pressures then alter these organic remains, driving off water and volatile compounds and concentrating the carbon in the remaining material.

Coal consists primarily of carbon, together with some oxygen and hydrogen, and smaller amounts of sulfur, iron, nitrogen and other elements. Variations in burial time, heat and pressure produce four basic commercial grades of coal: peat, lignite, bituminous (including subbituminous) and anthracite. Peat, a brown, crumbly precursor to true coal, contains only about 25 percent carbon.

But with longer burial times and increased heat and pressure, peat will alter into lignite, which consists of 30 to 40 percent carbon. Subbituminous and bituminous coal, called “soft coal,” contains 40 to 90 percent carbon and has a hardness of Mohs 2.0-2.5. Anthracite or “hard coal” consists of more than 90 percent carbon; at Mohs 2.5-3.0, anthracite is the hardest type of commercial coal.

The Origin of Jet

Jet is technically a rare type of lignite. While all commercial coals are derived from massive accumulations of plant matter and occur in seams ranging in thickness from a few feet to several hundred feet, jet is formed from individual tree trunks that became waterlogged, sank, and was buried in organic-rich sediments. Jet does not occur in massive seams, only in small, isolated pockets rarely more than a few inches in thickness.

Also unlike other types of coal, the structural and chemical nature of jet is influenced by the geochemical environment of the surrounding host rock, which is usually an organic-rich shale. As the jet develops, it absorbs oils and other hydrocarbon materials that are released by the decay of algae, plankton, and similar types of organic matter within the shale. Subsequently, the jet exhibits neither the extreme brittleness nor the extensive fracture systems common to other forms of coal.

At Mohs 3.0 to 4.0, the jet is by far the hardest type of coal. It is classified either as “hard jet,” which forms in marine environments, or “soft jet,” which develops in lacustrine or freshwater environments. All jet is opaque and exhibits a uniform, fine grain and a waxy-to velvety luster. It is easily carved and polishes to an attractive matte finish or a high sheen.

Jet consists of roughly 75 percent carbon, 12 percent oxygen, and lesser amounts of sulfur and hydrogen. It is easy to identify: when touched with a red-hot needle, jet emits a distinctive, coal-like odor.

A Jet History

Jet was collected and carved in Neolithic times. The oldest known jet artifact, recovered from a gravesite in Germany, dates to about 9000 B.C., making jet one of the oldest worked gem materials.

Whitby, located in Yorkshire in northeast England on the coast of the North Sea, has always been the world’s premier source of high-quality jet. The systematic collecting of jet for trading purposes had begun on the Whitby beaches by 1500 B.C. Jet later became especially popular among the Romans who obtained it from the same beaches.

Whitby jet, which is nearly altered to a subbituminous state, originated about 180 million years ago in a Jurassic Period saltwater swamp. The jet that washes onto the Whitby beaches is periodically replenished when North Sea storms erode the sea bottom. Some pieces of Whitby jet retain the shape of the original tree branches and trunks and are especially valuable as collector specimens.

By the time the popularity of jet jewelry peaked in England during the 1870s, collecting and working jet had become an industry in Whitby and a major part of the local economy. More than 1,000 Whitby residents were involved in collecting, working, or marketing jet, which was fashioned into cabochons and beads for jewelry, and into an array of small decorative objects, all of which were traded throughout the British Isles, Europe, and North America.

Jet the Gemstone

Part of jet’s popularity as a gem is because of its very low density. With a specific gravity of only 1.3-1.4, jet is half as dense as other black gemstones—a big advantage when wearing the long, bulky necklaces popular in Victorian Era mourning jewelry and the multiple-strand, “flapper” necklaces of the Roaring Twenties. Jet is also one of the few opaque gem materials that is commonly faceted.

Jet’s popularity in jewelry began fading during the 1930s in the face of competition from schorl (black tourmaline); dyed chalcedony; inexpensive imitations including black glass, plastic, and vulcanized rubber; and the growing acceptance of Art Deco jewelry styles which made little use of black gem materials.

Although Whitby remains the leading source of jet, this gem variety of coal is also found in Spain, France, Germany, Poland, Turkey, and Canada. In the United States, jet is found in Colorado and Utah where certain Native American groups continue to use it in jewelry and ceremonial objects, often in combination with turquoise and red coral.

Available today as beads, cabochons, and small decorative objects, as well as natural specimens, jet retains its distinctive identity as the rarest type of coal, one of the few organic gemstones and, thanks to William Shakespeare, an enduring simile for the color black.

This story about jet stone previously appeared in Rock & Gem magazine. Click here to subscribe. Story by Steve Voynick.

The post Jet Stone 101 first appeared on Rock & Gem Magazine.

For the last two weeks, I have been teaching advanced lapidary bench classes with the California Federation of Mineralogical Societies at their beautiful, forested site called Camp Paradise in the Sierra Nevada mountains. Multiple subjects are taught there including faceting, lapidary, advanced lapidary, soft stone carving, silversmithing, lost wax casting enameling and fused glass.

As a part of my classes, I teach making the tools used in carving the back and fronts of cabs. To my knowledge, these techniques are not commonly taught elsewhere.

Materials Needed

There are four different materials that I use to make my tools: 

• Wood dowels or wood wheels 
• Cratex rubberized wheels (with silicon carbide embedded into the rubber wheels) 
• Silicon carbide Mizzy wheels 
• Silicon carbide sanding blocks 

Wood Dowels

The wood dowels that I use are one-half-inch in diameter. If I have a small hole to work on I use a three-eighth-inch diameter dowel. I cut them into one-half-inch length pieces and drill a small hole into the end to accept the screw end of a half-inch threaded point mandrel. I then shape them by spinning the dowel in a flex shaft unit and applying a coarse wood rasp. I use these rounded shapes to sand and polish the decorative holes that I carve into the back of cabs. To sand the sides of a groove I shape the inside of a wood wheel and use tumbling grit for the sanding media.

Shaped Wheels

The second tool that I use is made from Cratex rubberized wheels. I shape them on a diamond T-bar stone wheel dresser by holding it at an angle to the back side of the spinning Cratex wheel. I use this wheel to sand the sides of a groove.

The third tool that I make is a shaped silicon carbide Heatless Mizzy wheel. It is shaped in the same manner as the Cratex wheel. This wheel is used to carve a groove in a cab.

Silicon Carbide Sanding Blocks

The fourth tools I use in my cab-making process are silicon carbide sanding blocks. They are made from silicon carbide material and are about three-eighth-inches square and four inches long. They come in various grits from about 220-grit through 600-grit. They also come in soft binder and hard binder which is determined by how the grit is bound together. I only use the hard binder. They are used to smooth out the lumps and low places in a carving after the grinding steps. I use them to round out the top shoulder and the V of a V-shaped groove. 

I cut up silicon carbide grinding wheels on my slab saw to make silicon carbide sanding blocks. When I have finished carving the top of rounded grooves on a carving, I shape the end of a silicon carbide carving block with a cylinder diamond bur to sand the top of the rounded grooves. 

I find that by making my own specialized tools I can make the work on my carvings go quicker and with a better overall outcome.

Steps By Photo

This story about making cabochons previously appeared in Rock & Gem magazine. Click here to subscribe. Story by Bob Rush.

The post Making Cabochons with Handmade Tools first appeared on Rock & Gem Magazine.

January

Garnet has been the birthstone for January since the 15th century, at least. With a Mohs hardness of 6.5 to 7.5, it can be faceted into beautiful gemstones that wear well in jewelry. Since the term “garnet” actually refers to a group of nesosilicate gems, those born in this month can choose from a rainbow of colors.

The most common members are red almandine, an iron-aluminum silicate; red pyrope, a magnesium aluminum silicate; orange-yellow spessartine, a manganese aluminum silicate; the yellow or green varieties of andradite, a calcium-iron silicate; predominately green grossular, a calcium-aluminum silicate; and rare, bright-green uvarovite, a calcium chromium silicate.

February

From the 15th century to the present, amethyst has been the preferred birthstone for February. Amethyst belongs to a mineral family that can compete with garnet for diversity of color: quartz.

Pure quartz is colorless, as exemplified by Herkimer diamonds. The causes of amethyst’s shades of pale violet to rich purple are radiation and the inclusion of iron impurities and trace elements.

As a rule, amethyst crystals are short and stubby, and occur in large numbers, often filling a large vug a hollow petrified tree section, or lining the inside of a geode. Fine crystals that are large enough to produce a faceted gem of over 20 carats are rare.

March

The current choice of a birthstone for March is aquamarine. Aquamarine is a variety of beryl (Mohs 7.5-8). Its name was derived from the fact that the beautiful, transparent, blue-green coloration of the gem resembles that of seawater. It can be found in translucent to transparent crystals that form in the hexagonal system. The six-sided crystals are often striated lengthwise.

Aquamarine develops in metamorphic rocks and, more often, in pegmatites.

April

Before 1900, a person with an April birthday had two choices of birthstone: diamond or sapphire. During the 20th century, however, diamonds became the preferred stone.

Diamond, a mineral consisting of pure carbon, heads the list of all gemstones for its beauty and hardness. A 10 on the Mohs Scale of Hardness, it is resistant to scratching and is an ideal gem to set in rings. Its hardness results from the arrangement of its atoms in cubes.

All diamonds have slightly rounded faces, and they’re so smooth they feel greasy to the touch. They can be colorless and water clear to blue, pink, yellow, brown, green or black, and transparent or translucent. They shine with an adamantine luster when held to the light.

May

There were two choices for May birthstones for several hundred years: emerald and agate. The popularity of agate seems to have waned at the turn of the 20th century, so emerald is now the favorite. It’s the green member of the beryl family of gemstones. The color varies from bright green to pale green and, sometimes, darker shades of blue-green.

Fine emeralds have a velvety surface appearance and, in the better stones, an even distribution of color. One bad trait of emeralds is a tendency to have inclusions. It’s rare to find an emerald without some slight imperfection. This in no way deters from the beauty of this gemstone, though. It can also be one way of determining whether an emerald is a simulated gem or the real thing, as manmade stones have no imperfections.

June

The contemporary choices for June are pearl, moonstone and alexandrite. Of course, a pearl is the organic product of marine bivalves and not a mineral.

Moonstone is a variety of feldspar that shows adularescence, or schiller, an optical effect that produces a milky luster with a bluish tinge that appears to move across the stone when it is tilted. The phenomenon is named after the feldspar variety adularia.

Alexandrite is a color-change variety of chrysoberyl (beryllium aluminum oxide). This is a very rare and expensive gemstone. It has a hardness of 8.5, and its crystals are either tabular or prismatic. The distinction between alexandrite and chrysoberyl is simply color. A strange characteristic of alexandrite is that it is red, purple or violet when held under artificial light, but in daylight, it looks green.

July

Ruby is the standard birthstone for the month of July. It is a corundum (aluminum oxide) gem that gets its color from the presence of chromium in its structure. An exceptionally hard mineral, corundum illustrates a hardness of nine on the Mohs scale. “Pigeon-blood” red is the preferred color for rubies, though they also occur in lighter shades, including pink. All other colors of corundum are called sapphires.

Ruby exhibits all the desirable properties of a jewelry stone: beauty, durability, optical properties, and rarity. Some rubies display a star or asterism when fashioned into a cabochon. This effect is caused by the reflection of light from numerous inclusions of minute, needle-like crystals of rutile. Corundum crystallizes in the hexagonal system with a tabular-barrel-shaped habit.

August

Current birthstones for August are peridot, the gem-quality form of olivine and spinel. Olivine makes up a large portion of the earth’s mantle. Rocks containing olivine have been brought to the surface by volcanic action and actually blown out in the form of volcanic bombs. Masses of olivine have been found in meteorites, and the Apollo astronauts brought basaltic rocks back from the moon that contained olivine.

A popular jewelry stone, peridot has a hardness of 6.5-7 and can be transparent or translucent, with a vitreous luster. Its color shades from deep green to apple green, yellow-green or olive. It’s most often found in granular nodules, forming short, prismatic crystals in the orthorhombic system.

Spinel is the gem-quality member of the larger spinel group. Its hardness (Mohs 7.5-8.0) makes it ideal for jewelry use. Its spectrum of colors includes red, pink, purple, blue and lavender. In times past, red spinel was often mistaken for ruby. A notable example is the Black Prince’s Ruby, set in the royal crown of England.

September

The birthstone for September is sapphire. This term refers to any corundum (aluminum oxide) gem that has any color other than red (ruby). Sapphires may be colorless, blue, green, yellow, orange, brown, pink, purple, gray, black, or multicolor. At Mohs 9, its hardness is second only to that of a diamond.

Heat treatment is sometimes used to give natural blue sapphires a deeper, more pleasing color. Natural star sapphires, which display the optical phenomenon of asterism, are very rare.

October

Two options for October are opal and tourmaline. Opal is a magnificent gemstone with a play of color or “fire” in all colors of the spectrum. Spaces between the tiny spherules of silica that make up the gem diffract light into its spectral colors. Red, yellow, green and blue, in strong to pastel shades, flash from the stone when it is tilted.

Opal occurs in common and precious types. Common opal does not display any reflective fire. It may have a honey-yellow, brown, gray or colorless body color that is milky and opaque. Opal (Mohs 5-6) is not a very hard gemstone.

Tourmaline, a silicate of boron, has a complicated chemical composition, in which a number of elements, including calcium, iron, sodium and aluminum, may combine. It has a Mohs hardness of 7-7.5.

It belongs to the trigonal crystal system and its habit is hemimorphic (a crystal having two ends of an axes unlike in its planes).

Because of the coloration of the individual stones, tourmaline has several names, including schorl (black), rubellite (red), indicolite (blue), and dravite (brown). Tricolor crystals are common. The popular watermelon variety has an outer layer of green around a red core.

November

The current birthstones for November are topaz and citrine. People tend to think of topaz, a silicate mineral with aluminum and fluorine, as a yellow stone, but heat-treating and color-enhancing adaptations have made blue the predominant color on the market. It is an allochromatic mineral, which means its color is caused by internal defects in the crystal and has a Mohs hardness of eight.

Citrine is the golden member of the quartz family (silicon dioxide). Though quartz in its many forms is one of the most abundant minerals on earth, fine, gem-grade crystals are not that common. Citrine is affordable and, when faceted, rivals more expensive gemstones in beauty.

December

There are three birthstones for December: turquoise, blue zircon and tanzanite. Turquoise (hydrated copper aluminum phosphate) is an opaque, blue-to-green, massive gem material. It has a relatively low hardness of Mohs 5-6, so care must be taken with turquoise jewelry.

The rarest and most valuable variety is robin’s-egg blue with black “spiderweb” veins of limonite. Fake turquoise, consisting of dyed howlite or magnesite, is common. Buyer beware.

Zircon (zirconium silicate) can be blue, black, red, brown, green, yellow, smoky, or water-clear. It has an adamantine luster much like that of a diamond, and it is often misidentified as such.

Tanzanite, the blue/purple variety of zoisite (basic calcium aluminum silicate), is a recently introduced alternative for December. Tanzanite crystals in shades of yellow to brown, green, pink, gray or blue are often heat-treated to produce a gemstone that is a beautiful and permanent blue.

This story about what are birthstones by month previously appeared in Rock & Gem magazine. Click here to subscribe! Story by Kenneth H. Rohn.

The post What are the Birthstones by Month? first appeared on Rock & Gem Magazine.

The largest, hottest and driest of the national parks in the United States, Death Valley provides stunning views of a vast desert that includes incredible geological sites you won’t see anywhere else. It is truly exceptional.

Geologic Forces in Death Valley National Park

“The number of geologic forces at work in Death Valley makes it unique,” says David Blacker, executive director of the Death Valley Natural History Association. “Erosion, faulting, the pull of the basin and range formations — add a double rain shadow (an area of significantly reduced rainfall behind a mountainous region), and you get a unique landscape that has to be seen to believe.”

Death Valley’s features include deep valleys, high mountains and a variety of unusual rock formations that have developed over millennia. To stand in Death Valley is to look through a window into the past.

“The earliest Death Valley rocks were sedimentary, and deposited about 2.5 billion years ago, while the area we know as Death Valley was under a shallow sea,” says Blacker. “Ten million years, ago Death Valley was a Lowland Basin with grasslands. Of course, over that time it has become much more arid, and the double rain shadow has locked it in as the hottest and driest place in North America.”

Exploring Death Valley National Park

While it can take years of backcountry exploration to discover all the geological wonders of Death Valley National Park, a handful of spectacular sites provide vehicle access to visitors who want to get a taste of what this amazing place has to offer.

Artists Palette

One of the easiest to get to and most beautiful spots in Death Valley National Park is the Artists Palette. Made up of hills splashed with the colors of red, green, orange, yellow, purple, pink and blue, the Artists Palette was created from volcanic deposits rich in iron oxides and chlorite. Iron compounds produce red, pink and yellow colors, while the decomposition of tuff-derived mica produces green. Manganese produces purple and blue.

Formed during the Miocene age, the hills are made of cemented gravel, playa deposits and volcanic debris, which is 5,000 feet thick in places. The colors were created by chemical reactions during various forms of weathering.

The hills themselves were formed by water erosion and can be viewed from the ninemile Artists Palette Drive, a winding, paved road that gives visitors a chance to experience this phenomenon up close. The best time to see the hills is at sunrise and sunset when the angled sunlight provides brighter colors on the rocks—although the colors are stunning at any time of day. Nearby salt flats and the striking Black Mountains are also visible from the road.

Zabriskie Point

Most visitors to Death Valley National Park go to Zabriskie Point to take in the views of the surrounding landscape at sunrise and sunset. But those interested in the site’s geological treasures will appreciate this spot at any time of the day.

The badlands visible from Zabriskie Point make up the 7,000-foot thick Furnace Creek Formation, which consists of saline muds, gravels from nearby mountains, and ash from the once-active Black Mountain volcanic field. The formation appears as tan-colored sandstone and clay rocks showing deep erosion, with dark-colored rocks on the ridgelines that were created by volcanic eruptions. Look to the west and you will see Red Cathedral, a geological formation of steep cliffs composed of red-colored oxidized sandstone.

Zabriskie Point is easily accessible to visitors, with a large parking area just off the main park road and a short walk to a vista point. To avoid the crowds, plan to see it in the middle of the day since most people visit Zabriskie Point at dawn and dusk.

Badwater Basin

The lowest point on the North American Continent, Badwater Basin is more than just an anomaly at its depth of 282 feet below sea level. It is also an endorheic basin, which means water that gathers here does not flow to any external bodies of water. Over tens of thousands of years, water that collected here only left the basin through evaporation. The result is a 200-square-mile basin floor made up of mostly sodium chloride—table salt—with calcite, gypsum and borax thrown in. This accumulated sediment and salt is more than 11,000 feet deep.

You can view the expanse of this snow white salt from a platform just off Badwater Road, or venture onto it by walking on a boardwalk that stretches one mile across the basin floor. The cliffs of the Black Mountains are just behind you to the east, and you’ll see a marker on a cliff showing how far you are standing below sea level. To your west, the towering 11,039-foot Telescope Peak rises out of the valley floor, giving you a dramatic perspective you won’t see anywhere else in North America.

Be sure to look into the tiny and highly salinized spring located near the beginning of the boardwalk. It is home to the Badwater snail, an endangered fish that lives nowhere else on Earth.

Ubehebe Crater

Located in the northern section of Death Valley National Park, the Ubehebe Crater is a 600-foot-deep hole in the ground. Caused by a volcanic eruption that took place about 2,000 years ago, the half-mile diameter crater is the product of a maar (explosion pit) volcano. The Ubehebe Crater resulted when molten lava came into contact with groundwater at about 200 feet below the surface. The heat from the lava caused the water to flash into steam, creating incredible pressure that built up and exploded outward, leaving the massive crater in its wake.

As you drive from North Highway up to the Ubehebe Crater parking area, you’ll see cinders from other similar volcanic explosions covering much of the surrounding area. Just north of Ubehebe and other surrounding craters, you can see cinders on the dry bed of ancient Lake Rogers, located on the valley floor. The cinders covering most of the area came from the Ubehebe Crater, and are 50 feet thick at the crater rim.

Colorful layers in the crater’s eastern wall are the result of the explosion. The alluvial fan inside the crater includes fanglomorate, as well as sandstone and older conglomerate deposits, loosely cemented together by calcite. Most of the rock inside the crater is either volcanic or metamorphic.

The moderate, 1.5-mile Ubehebe Rim Trail loops the rim of the crater and provides views of the sedimentary layers left behind by the explosion. If you want to get closer to the interior of the crater, a more rugged trail descends to the bottom.

Racetrack Playa

Since Death Valley National Park’s creation in 1933, both visitors and scientists have wondered over the phenomenon of the Racetrack Playa. This level, dry lakebed is home to rocks made from dolomite and syenite—the same minerals found in the surrounding mountains. The rocks weigh from a few ounces to several hundred pounds and are called the Sailing Stones because they show evidence of movement across the dry lake bed. While observers have not seen the rocks actually moving, trails in the mud-cracked sediment and changes in the rocks’ location indicate they are anything but stationary.

In 2014, scientists conducted research that seems to explain what makes the rocks move. Water coming down off the adjacent mountains settles in the lakebed, and then freezes, creating a thin layer of ice. When slight winds blow while the ice is present, the rocks slide, leaving a trail in the mud.

Although this may have solved the mystery, the Racetrack Playa is still a sight to behold. Head there from Ubehebe Crater, which is several miles to the north. You’ll need a 4-wheel drive vehicle with high clearance to drive the road that leads to the Racetrack from Furnace Creek, and is only recommended in the wintertime.

Death Valley National Park – A Rockhound Destination

When it comes to geological wonders, few places on Earth can compete with the splendor of Death Valley National Park. Not only it is a spectacular destination for rock hounds, it’s also a goldmine for researchers who want to learn about the geological history of the planet.

“The climatic conditions make it an ideal geologic laboratory because the lack of vegetation makes it so there is little to obscure rock characteristics,” says geologist Gregg Wilkerson, co-author of Roadside Geology and Mining History of Death Valley. “Over the next million years, the pull-apart basin will continue to grow, the valley will get broader and the mountains will get higher.”

Death Valley has been around since long before humans walked the Earth, and will likely still be there after we are gone. Spending some time in this amazing place will leave you with a sense of awe that will last a lifetime.

This story about the geology of Death Valley previously appeared in Rock & Gem magazine. Click here to subscribe! Story and photos by Audrey Pavia.

The post Death Valley National Park Geology first appeared on Rock & Gem Magazine.