Nevada Gemstone Mining
Nevada was once the leading state for turquoise. Virgin Valley has become world-famous for black opal.
Author: Hobart M. King, Ph.D., GIA Graduate Gemologist
Gold and Gems to Go With It
Nevada is the leading gold producer in the United States. No other state is even close. In addition, Nevada is one of the leading gemstone-producing states. Nevada mines produce opal, turquoise, variscite and a wide range of other gem materials.
Table of Contents
A Diversity of Small Gem Deposits
The gemstone that Nevada is best known for today is opal. Some of the finest black opal in the world is mined in the Virgin Valley area in the northwest corner of the state. There, millions of years ago, a volcanic eruption blanketed the land with ash and buried a nearby forest. Today parts of Virgin Valley are underlain by opal-bearing tuff and volcanic ash from that eruption which are over 100 feet thick.
Some of the buried wood was petrified when groundwater carried in dissolved silica. The silica precipitated in the open spaces of the wood and replaced the woody material. Some of the silica formed beautiful precious opal. The Royal Peacock, Bonanza, and Rainbow Ridge Mines are all locations where precious opal is currently produced. All three are fee mines, open during limited times of the year for public digging. There you can pay a small fee, look for opal (and other gem materials) and keep whatever you find according to mine rules.
Fire opal is also found in Virgin Valley. "Fire opal" is a term used for a colorful, translucent to transparent opal with a background color that is a fire-like hue of yellow to orange to red. A piece of yellow faceted Nevada fire opal is shown on this page.
The most frequently found type of opal in Virgin Valley is common opal. Common opal does not exhibit the play-of-color seen in precious opal or the translucent to transparent hues of fire opal. In the column at right, we have a photo of some cream and black mossy opal from the Royal Peacock Mine. Although most opal will exhibit a weak fluorescence under ultraviolet light, some of the common opal from Royal Peacock has a spectacular green fluorescence.
One problem that is frequently seen in Virgin Valley opal is crazing. The material looks sound when it is removed from the ground, but after a few years of exposure, cracks will develop and the opal will break into small pieces. Some cutters "age" their rough for a few years before cutting to be sure that their cutting time is well-spent.
Some of the opal found in Virgin Valley is uraniferous. In the early 1950s, the Atomic Energy Commission asked the United States Geological Survey to sample and evaluate the material. They found uraniferous opal in discontinuous layers parallel to the bedding of the ash and tuff deposits. Most of the opal examined contained between trace amounts and 0.02 percent uranium. One sample containing 0.12 percent uranium was reported. (Information about the USGS study can be found in: Virgin Valley Opal District Humboldt County, Nevada, by M.H. Staatz and H.L. Bauer, United States Geological Survey Circular 142, 1951.)
Nevada became a major producer of turquoise in the 1930s, and until the early 1980s, Nevada was the leading producer of turquoise in the United States. Turquoise has been produced from dozens of small mines. Some of them have produced over $1 million in rough. A few small mines continue to be worked today, mostly part-time by a few employees or partners.
Nevada turquoise is found in thin veins, seams, and nodules. Some material is hard, solid rough that cuts well and accepts a great polish. Other material must be stabilized with backing or resins to produce a good cabochon.
Nevada turquoise occurs in the typical range of blue, blue-green and greenish colors, with iron-rich specimens being on the green end of the color range. Specimens with and without matrix are found. Variscite and faustite are often found associated with the turquoise and are occasionally produced as gem materials.
There are some reports of "white turquoise" and "white buffalo turquoise" being mined in Nevada, and a lot of material is sold under those names. Turquoise can be a very light blue or a very light green and sometimes a yellowish green. But the copper content of genuine turquoise should prevent it from being a snow-white color. We purchased some material sold as "white turquoise," sent it for x-ray diffraction, and learned that it was a combination of magnesite and dolomite. Others report that material sold as white turquoise is howlite or opalized calcite. So, much of the material being sold as "white turquoise" or "white buffalo turquoise" would be better if it was called "white buffalo stone" because it is not turquoise.
Variscite is an aluminum phosphate mineral with a chemical composition of AlPO4•2H2O. It occurs in a range of green, yellowish green, yellowish brown and slightly bluish green colors. Nevada variscite sometimes contains brown or black matrix that is very similar to the matrix of turquoise.
Variscite has been produced in small amounts at a few locations in Lander County, Nevada. Some is found as nodules, and much is found as a vein and fracture-filling material. It is sometimes associated with turquoise as both minerals form above the water table, in the near-surface environment, and require a source of phosphate.
Nevada variscite is often cut and polished into beautiful cabochons. Some cutters prepare their variscite for cutting by gluing it to a thin piece of black plastic or other material. The glue and the stiff backing material provide stability to the sometimes-fragile variscite. This style of cabochon is properly described as a "doublet" - meaing that it is a composite of variscite attached to a second material.
Nevada variscite has been confused with turquoise because their color ranges have a slight overlap and because of their similar appearance. The two minerals can easily be separated using the standard gemological tests described here.
A Diversity of Small Gem Deposits
A number of other gem materials have been mined in Nevada. The state is well-known for its many small deposits of petrified wood, agate, jasper, and obsidian. Nevada is also a source of wonderstone, which is a variety of colorful rhyolite that often contains beautiful swirl and flow patterns.
Beryl, faustite, nephrite, magnesite, rhodonite, topaz, and vesuvianite have all been found in Nevada.
|Ruby and Sapphire|
|Pictures of Opal|
|Canadian Diamond Mines|