Stones and Minerals

Since I use so many, I figured I’d start to post some information on the stones I use the most. It is very much a work in progress.

For reference books I’d suggest Walter Schumann’s Gemstones of the World as a good place to start. It’s got a little bit of information about seemingly everything. For more standard gemstones Antionette Matlins’ Colored Gemstones gives more information about each gem. The Smithsonian guides can also be useful, though I feel like they sometimes use too much terminology with too little explanation.

Amethyst is a purple quartz species, hints of iron give it its color. Mohs’ 7 Its name comes from the Greek for ‘not drunk.’ The ancient Greeks (and Romans) attributed its color to Dionysus, the god of wine. Like all myths it has several variations (normally the other thing all myths have in common is that maiden+Greek god=bad), but the basics version is that Dionysus was in a killing temper and came across a maiden named Amethyst. She was turned into a white stone by one of the goddesses in order to spare her from his wrath, and when he calmed down he poured a libation of wine over the stone in remorse, staining it purple. Why the god of wine’s stone would keep you sober is beyond me… (One theory is that cups made of amethyst made watered wine look richer.)

Ammonite is a replacement fossil of any of various species of long extinct cephalopods. They were a family of carnivorous species that lived in the seas from 300-65 million years ago. Their fossils are fairly common, and can be extremely beautiful, ranging from rich colored cross sections that show detailed chambers, to surfaces that have a sheen of mother of pearl, to textures like fractals and fall leaves, or in their most extreme case, essentially opalised into rich colored surfaces called ammolite. Ammonites were named after their ram horn shape after the Egyptian God Amon who is often portrayed with ram’s horns.

Charolite (sometimes Charoite)- Mohs’ 4.5-5 Fairly new to the market and somewhat rare mineral. The dramatic purple with occasional chatoyancy is natural. When imported from Russia already cut, they are often set against a slab of black jade.

Chrysocolla is a copper silicate. Because of the copper its colors stay in the green/blue range with occasional black or brown inclusions. It’s often described as having a vitreous or greasy luster. At a Mohs’s 2-4 it’s a relatively soft stone. It is often associated with other copper ores like azurite, malachite and limonite.

Geodes are partially filled hollow cavities in rock that are lined by minerals. A hollow is formed in geologic upheaval and over time solutions containing dissolved minerals can filter in and leave deposits within the hollow, often resulting in layers of agate then quartz and/or calcite crystals. Studying the order of the layers can give a window into the geologic history of the area in which the geode is found.

Iolite– Mohs’ 7-7.5 You might have run across iolite in the past under the name water-sapphire (though it is *much* softer than true sapphire) or the more fun title of viking’s compass. It gets its name from the greek work for violet, but its color changes depending on the angle of the light. With its lovely mix of violet/blue/grey it is sometimes confused with the much rarer gemstone tanzanite.

Kyanite– Mohs’ 6-7 Its name is derived from a Greek word for dark blue (think cyan). Kyanite normally has irregular streaks of color, even in gem quality stones.

Labradorite is a type of feldspar, sort of a cousin to moonstone. Mohs’ 6-6.5 Named after the Labrador peninsula in Canada, Labradorite from anywhere else is properly called spectrolite. (Though it is misused so often, most of us are bad about being specific, and spectrolite is sometimes used just for the highest quality Finnish material.) The shimmer of color in Labradorite is called labradorescence. I’ve seen different versions of myths that say the color in Labradorite comes from some of  the aurora borealis trapped in stone.

Lapis lazuli is composed of a combination of several different minerals in varying concentrations. The golden sparkle comes from pyrite in the stone. Its blue color mostly comes from sulfur. Mohs’ 5-6

This is one of the oldest recorded gemstones. It has been mined in Afghanistan for over 6000 years. In the middle ages it was ground up (*shudder*) for use in the highest quality blue pigments. It’s sensitive to high pressure, hot water, and both severely acid and base environments. So take it off before you work out or shower.

Larimar is a type of blue pectolite found only in the Dominican Republic. Mohs’ 4.5-5

Malachite is a copper carbonate that forms near copper ore deposits. Mohs’ 3.5-4 Its name is assumed to derive from the Greek for either malache-mallow plant or malakos-soft. Both are appropriate. Like lapis, malachite has a long history. It was used in ancient times for amulets and jewelry as well as eye shadow. It too, was used for pigments in the Middle Ages. An easily scratched but beautiful colored stone, so treat it kindly and enjoy.

Moonstone is a type of feldspar. Mohs’ 6-6.5 It comes in several varieties, rainbow has a clear or white base with a rainbow shimmer across it, others are grey or peach with a white shimmer. The most expensive is a rich blue color. The shimmer of color in moonstone is known as adularescence.

Opal is a hydrated silicon dioxide. Mohs’ 5.5-6. I normally use boulder opal, which has veins of opal running through a harder rock matrix; or doublets, which are a slice of opal against a darker and stronger background (normally ironstone). These guys can dry out, so be kind to them and don’t leave them in direct sun or anywhere super hot/dry for an extended period of time.  It’s the hydration between tiny silicon spheres that gives opal it’s fantastic flash and fire. Fancy jewelry stores keep tiny cups of water in case with the opals to help balance the humidity.

Orthoceras is a genus of extinct cephalopods which are fairly well represented in the fossil record. They are again an example of a replacement fossil. Though in the nautiloid subclass they were long and straight in shape, with the fossils often looking like pale bullets shooting through the dark rock. They went extinct around 450 million years ago.

Peridot is a pale to middle green mineral, normally with yellow undertones. (The richness of color depends on the iron content.) Mohs 6.5-7. Scratchable, but strong enough to use for rings. It is almost never treated, so chances are the peridot color you see is natural. It is the only semi precious stone found in meteorites.

Pietersite is essentially brecciated (broken up and squashed back together) tiger’s eye.

Ruby is a red corundum. (All other shades of corundum are called sapphires.) It is an extremely hard gemstone, and its most desired shade is a vibrant, true red with no inclusions. However, there are exceptions to every rule, and inclusions called silk sometimes align into stars and are then quite desirable.

Seraphinite (also called Clinochlore)- Mohs’ 2-4. Also newer to the market and hailing from Russia, Seraphinite has a similar texture to charolite, with rich colors and paler chatoyant veins. It’s fairly soft, so best used for earrings and pendants.

Spectrolite is the proper name for labradorite mined anywhere other than Labrador. Less properly, I was first introduced to it as simply the highest quality labradorite, and many use it in that sense.

Tiger’s Eye is an asbestos/crocodilite pseudomorph. Basically quartz crystals slowly replace the structure of asbestos, leaving behind a mostly quartz rock with fine shimmer showing the texture of the former tenant. Its first stage is the blue-ish version known as hawk’s eye or blue tiger’s eye, and the better known golden tiger’s eye occurs when the iron from the original material oxidizes. The shimmer between the planes (the cats eye effect) is known as chatoyancy.

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8 responses to “Stones and Minerals

  1. Pingback: Fossil Record « Magpie's Miscellany

  2. Love your post of Stones and Minerals which I myself collect. I also collect fossils. However not many fossils in the area around where I live. East Crete.I go back to England now and again, Much Wenlock and all around the Ludlow area in Shropshire England is great for fossils.

    • I live in the northeastern US, which is also not a good place for fossil collecting. Most of mine I’ve purchased over the years. I’ve been to England but never those areas. I’d love to go someday, I’m trying to keep track of the different good fossil collecting areas for vacation ideas. I’ve always hears Shropshire was beautiful anyway 🙂

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