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Read Ebook: Natural Gemstones by Geological Survey U S
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Coral Formed mainly of calcite or conchiolin, a horny organic substance Specific gravity: 2.60-2.70
Each coral polyp, a tiny marine animal that lives in enormous colonies, extracts calcium carbonate from the sea and exudes it to build a protective home around and above itself. Each generation of polyps dies in its protective home and each succeeding generation builds on top of its predecessor.
Gem coral ranges from semitranslucent to opaque and occurs in white, pink, orange, red, blue, violet, golden, and black. The black and golden corals are largely horny organic substances, not calcium carbonate.
The finest coral is used to make figurines, cameos, carvings, and beads.
Jet Carbon plus various hydrocarbon compounds Specific gravity: 1.30-1.32
This compact velvet-black coal takes a good polish and is often cut into beads, bracelets, and a wide range of decorative and useful objects.
Natural pearls come in various shapes: round, pear, drop, egg, and others. They also come in various colors, such as white, cream, light rose, cream rose, black, gray, bronze, blue, dark blue, blue green, red, purple, yellow, and violet.
Buyer beware
Inexperienced buyers must take whatever steps are needed to ensure that gems they intend to purchase are exactly what the seller purports them to be and that they are being offered at a fair market price.
More and more synthetic gems--and inferior grades and cuts of natural gems--are being sold to unwary buyers by unscrupulous sellers.
Since 1935, the mining of gemstones in the United States has been almost entirely a recreational activity of mineral collectors and hobbyists.
In recent years, very few individuals have derived their entire income from gemstones mined by themselves.
This is not to say that the proprietors of roadside rock shops buy all of their stock from others. Rock shops are abundant in areas of the United States that are rich in gem materials, and the shops tend to specialize in the local gem commodities, most of which the proprietors gather.
Rather than doing the mining themselves, owners of land that has a deposit of gem-quality minerals sometimes charge hobbyists for the right to collect gemstones. For example, diamond in Arkansas, opal in Idaho, and agate in Oregon and Washington are mined by hobbyists under this "fee digging" arrangement.
However, the flow of money into the local economy by paying these small fees and by the purchase of gemstones is minor compared to the money the enthusiasts spend for lodging and other living expenses while visiting an area to dig for gemstones.
Several kinds of natural gemstones have been found in every State of the United States, but much larger deposits of the most precious kinds are found outside the United States.
The 1990 U.S. output of natural gemstones was primarily from Tennessee, California, Arizona, Arkansas, Montana, Nevada, and Maine.
An estimated 80,000 visitors found a total of 315 carats of diamonds in the Crater of Diamonds State Park in Arkansas. There were sizeable yields of freshwater pearls in Tennessee, turquoise in Arizona and Nevada, tourmaline in Maine, and tourmaline, kunzite, and garnet in California.
Gemstones: Value of U.S. production vs. imports, 1986 and 1989
Production 1986 1989 Natural .3 million .0 million Synthetic 10.3 23.5 .6 .5 Mine employment 300 800 Imports for consumption: .18 billion .00 billion Apparent reliance on imports over 99% 98% exports
Estimated.
Including freshwater pearls natural, and cultured.
U.S. production of commercial gems includes agate, beryl, freshwater pearl, garnet, jade, jasper, mother-of-pearl, opal, peridot, quartz, sapphire, tourmaline, and turquoise.
Except for the few gem diamonds found each year in Arkansas, U.S. diamond production is very low.
Yet exploration for diamonds continues in Alaska, Colorado, Michigan, Minnesota, Wisconsin, and Wyoming. A diamond mining project at the Crater of Diamonds State Park in Arkansas is still being evaluated by the State.
World diamond reserves are estimated to be about 300 million carats, including near-gem materials but not diamonds of abrasive quality.
Most of the reserves are in southern Africa, Siberia, and western Australia. It is difficult to estimate reserves because the value of a given deposit varies with the market for the gems.
Chemical formulas of gemstones
Some ways to contact a local rock, mineral, or gem club
Talk to a member of the geology or earth science department of your local college or university.
Talk to a member of the science department of your local high school.
Write to the--
Eastern Federation of Mineralogical and Lapidary Societies Box 10119 Alexandria, VA 22310-0119
or the
Midwest Federation of Mineralogical and Geological Societies 306 Somonauk Park Forest, IL 60466
Check the phone book for your nearest rock and mineral shop and talk to the owners.
Role of the U.S. Geological Survey
The USGS reports deposits that seem likely to contain gemstones. It is not a function of the USGS to exploit such resources.
USGS geologists perform continuing research on kimberlites, the initial source of diamonds. Not all kimberlites are diamond-bearing, and some of the research is directed to learning what indications you look for during exploration to distinguish fertile from barren kimberlite. USGS geologists are compiling a U.S. map showing the locations of known kimberlites.
Selected general references
A trip to your local library is the best first step toward understanding gemstones and toward planning a trip to gem and rock shops or to places where you may be able to collect gemstones.
The guides in Section I tell about equipment needed for collecting, etiquette of collecting, map reading, organizing a collection, collecting localities by States, mineral societies, mineral show dates and locations, and rock, mineral, and fossil dealers.
The references below focus mainly on natural gemstones and the gems made from them rather than on synthetic gemstones, rocks, or other nongem minerals.
Acknowledgments
The U.S. Geological Survey is grateful to the following individuals for their assistance:
Harvey E. Belkin, Geologist, Geological Survey, U.S. Department of the Interior, Reston, VA.
Jane Jenness, Minerals Information Office, U.S. Geological Survey, Washington, DC.
Photographs
All photographs are courtesy of The Smithsonian Institution.
Transcriber's Notes
--In the ASCII version only, subscripted numbers are preceded by underscore and delimited by brackets.
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