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January-February 2010

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U.S. Gemstones: An Overview

Most mineral collectors, even those from other countries, are fully aware of the richness of the United States with respect to gem deposits, but the average consumer of gems surely has no idea of the wealth of gem material that has been and is still being extracted from the earth in this country. I suspect that the diversity of gems found here easily rivals that of any other country in the world, although in terms of the volume of gems produced, we fall far behind Brazil and Madagascar, and possibly even India, Tanzania, Myanmar, Afghanistan, and Russia. These domestic deposits are spread across the entire country, literally from coast to coast. To underscore this, there are major tourmaline mines in New England (principally Maine) and California, with virtually no important tourmaline source in between. Gem-quality amethyst and smoky quartz are found in dozens of states. There is a semicontinuous belt of amethyst occurrences, much of it of faceting quality, in the foothills of the Appalachian Mountains, stretching all the way from Maine to Georgia (White and Cook 1990), and a sporadic source of superb gem amethyst in the mountains just east of Phoenix, Arizona. Superb amethyst specimens and gem rough are currently being mined at Jacksons Crossroads, Wilkes County, Georgia. The more familiar and more highly regarded gems—emerald, diamond, sapphire, turquoise, opal, aquamarine, garnet, and nephrite jade—are well represented by significant deposits. Less familiar to the general public but nevertheless found in relative abundance in this country are peridot, sunstone, kunzite, morganite, amazonite, agate of all sorts including fire agate, jasper in various forms, rhodochrosite, and malachite/azurite. Of greatest appeal, however, among the lesser-known gems are two that are found only in the United States: benitoite from California and red beryl from Utah. There is, arguably, a third, hiddenite, which is an emerald-green variety of the mineral spodumene, that occurs in North Carolina.

Figure 1. Amethyst, Four Peaks, Arizona. This flawless gem weighs 39.4 carats and is 22 × 19 mm. Tino Hammid photo.

Figure 1. Amethyst, Four Peaks, Arizona. This flawless gem weighs 39.4 carats and is 22 × 19 mm. Tino Hammid photo.

Figure 2. Tourmaline (elbaite) from the Dunton mine, Newry, Maine. A selection of some of the crystals, and stones cut from them, that were found in the extraordinary pocket discovery of 1973. Wendell Wilson photo.

Figure 2. Tourmaline (elbaite) from the Dunton mine, Newry, Maine. A selection of some of the crystals, and stones cut from them, that were found in the extraordinary pocket discovery of 1973. Wendell Wilson photo.

Tourmaline

Gem tourmaline (the species elbaite exclusively) occurs in pegmatites in both Maine and California. Glassy green fragments were found at Mount Mica, Paris Hill, Oxford County, Maine, in 1820 among the roots of a fallen tree, leading to active mining for gem tourmaline for the first time in this country. Much of the production throughout the latter part of the nineteenth century was sold to Tiffany & Co. in New York. A major discovery occurred at the Dunton mine, Newry, Oxford County, in 1972, consisting of a series of pockets that yielded far in excess of 1 metric ton of loose tourmaline crystals and crystal fragments, a very large percentage of which was facet grade. The other major tourmaline producer, Mount Mica, is still being worked today, but Newry ceased production not long after the big 1972 discovery.

Figure 3. The Hamlin necklace. Most of the eighteen major stones are from Mount Mica, Maine, including the large green one, which weights 34 carats. Some of the stones are beryl from Massachusetts. The necklace dates from the late nineteenth century and was commissioned by A. C. Hamlin, one of the family of Hamlins who discovered and mined the property. Harvard Mineralogical Museum necklace. Tino Hammid photo.

Figure 3. The Hamlin necklace. Most of the eighteen major stones are from Mount Mica, Maine, including the large green one, which weights 34 carats. Some of the stones are beryl from Massachusetts. The necklace dates from the late nineteenth century and was commissioned by A. C. Hamlin, one of the family of Hamlins who discovered and mined the property. Harvard Mineralogical Museum necklace. Tino Hammid photo.

Figure 4. A faceted 4.15-carat tourmaline (elbaite) from Mount Mica, Maine; cut by John Bradshaw. Tino Hammid photo.

Figure 4. A faceted 4.15-carat tourmaline (elbaite) from Mount Mica, Maine; cut by John Bradshaw. Tino Hammid photo.

Figure 5. Pink and green tourmaline (elbaite) from the Himalaya mine, San Diego County, California. Tino Hammid photo.

Figure 5. Pink and green tourmaline (elbaite) from the Himalaya mine, San Diego County, California. Tino Hammid photo.

Legend has it that in Mesa Grande, California, in the 1860s, a salesman noticed Indian children playing with blue, green, and red “marbles,” leading to the discovery of gem tourmaline pegmatites in several places in southern California. Most of the faceting-grade pieces went to cutters in New York or San Francisco, but tons of carving rough were shipped to China where it was made into snuff bottles, figurines, and so forth. One fascinating figure stands out—between 1902 and 1910, 120 tons of tourmaline valued at $800,000 were mined from the Mesa Grande area, mostly the Himalaya mine. In terms of record stones, the Tourmaline Queen mine, Pala, San Diego County, California, produced rough that resulted in a dark pink rubellite weighing 509 carats. Mines in both Maine and California have sporadically continued to produce gem crystals right up to the present time, and the quality of these gems matches that of most other deposits around the world.

Emerald

When the public reads or hears about American gemstones, the news almost always relates to emeralds from North Carolina or diamonds from Arkansas. It is true that some lovely gem emeralds have been faceted from green beryl crystals mined in North Carolina, but the production since the discovery of the deposit in the vicinity of Hiddenite (named for the gem), Alexander County, has been modest when compared to other worldwide major sources of gem emerald. The first emerald crystal suitable for cutting was found by J. Adlai D. Stephenson of Statesville, in 1875, and this area has also been mined sporadically ever since. It is, in fact, being mined for emeralds and hiddenite today, with a level of production that probably exceeds all earlier efforts. There was for a time another emerald mine in North Carolina, the Crabtree deposit on Big Crabtree Mountain, Mitchell County, but it produced few transparent stones that could be cut into gems.

Figure 6. Beryl, variety emerald, from the Rist mine, Hiddenite, Alexander County, North Carolina; 12.7 cm high. Houston Museum of Natural Science specimen, Jeff Scovil photo.

Figure 6. Beryl, variety emerald, from the Rist mine, Hiddenite, Alexander County, North Carolina; 12.7 cm high. Houston Museum of Natural Science specimen, Jeff Scovil photo.

Diamond

The first Arkansas diamond was found near Murfreesboro, Pike County, Arkansas, in 1906. As of today more than 75,000 diamonds have been removed from the kimberlite there, but no commercial production has occurred, and it is unlikely that it ever will, particularly as the area has been made into the Crater of Diamonds State Park, where visitors pay a fee and are allowed to search for diamonds. Most of the diamonds found there are very small, but in September 2008 a 4.68-carat crystal was discovered. The largest diamond reported weighed 40.23 carats, and it was found before the site became a park. It was named the “Uncle Sam Diamond.” The largest recovered since the area became a park weighed 16 carats. In all, some 612 diamonds were found in 2008 by visitors to the park.

Commercial diamond mining was begun at the Kelsey Lake mine in Colorado in 1995, and about half of its production was considered gem quality, but the mine was closed in April 2002. A few notable crystals were cut into gems and sold for large sums of money.

Figure 7. The “Sunshine” Diamond from Crater of Diamonds State Park, Murfreesboro, Arkansas; 5.47 carats. Jim Houran specimen, Jeff Scovil photo.

Figure 7. The “Sunshine” Diamond from Crater of Diamonds State Park, Murfreesboro, Arkansas; 5.47 carats. Jim Houran specimen, Jeff Scovil photo.

Sapphire

The sapphire story is even more interesting. In 1860 prospectors found gold and “blue pebbles” along the Missouri River northeast of Helena, Lewis and Clark County, Montana. In 1894 they sent a vial of these to a friend in Maine who wrote back thanking them for the gold and the sapphires, to which the prospector replied, “What the hell is a sapphire?” Sapphires are found in gravels that cover broad areas of Montana, with many of these deposits being as thick as 40 feet. They have been dredged for gold, and in the process large quantities of sapphire were produced as well. In fact, the total production of industrial and gem sapphire from Montana has been estimated at $3–5 million (Sinkankas 1959). The sapphires have been eroded out of their mother rock and deposited in these gravel bars. The most productive sites for sapphire in Montana are spread over much of the state, from its center to a large portion of the southwestern section. The famous Yogo Gulch, known for its cornflower-blue stones, is the easternmost deposit. Others that have produced notable amounts of sapphire include the Rock Creek area and various gravels along the Missouri River, including Eldorado Bar, the Emerald Bar, Magpie Gulch and the American Bar, and the gravels of Dry Cottonwood Creek. Yogo Gulch has produced by far the greatest volume of gem sapphire of fine color, perhaps because it is the only source in Montana that involved actual mining of rock, much of it underground, instead of dredging for gold where the sapphires were a byproduct.

Most active mining in conjunction with dredging for gold occurred in the latter part of the nineteenth century, with some deposits seeing sporadic activity into the first part of the twentieth century. Throughout much of the latter part of the last century, a number of large and small corporations had a go at mining Yogo Gulch, but with only limited success, often in spite of grand publicity promotions. It should be noted that the vast majority of the sapphires recovered from all mining in Montana were of inferior quality and were sold for industrial use only. The stones of gem quality tended to be small; the largest fine cut stone of which I am aware is an unheated blue weighing 18.10 carats, from the El Dorado Bar, Lewis and Clark County.

Figure 8. Sapphire workings at the El Dorado Bar, Lewis and Clark County, Montana. Bob Jones photo.

Figure 8. Sapphire workings at the El Dorado Bar, Lewis and Clark County, Montana. Bob Jones photo.

Figure 9. Faceted sapphires from Montana. Tino Hammid photo.

Figure 9. Faceted sapphires from Montana. Tino Hammid photo.

Figure 10. A selection of sapphire rough from Rock Creek, Granite County, Montana, showing the various colors found there. Bob Jones photo.

Figure 10. A selection of sapphire rough from Rock Creek, Granite County, Montana, showing the various colors found there. Bob Jones photo.

Peridot

Peridot has long been known to occur in basalt rock in various places in Arizona. It was a common associate of the widely advertised red garnets found on the surfaces of ant hills in Apache County and sold for much of the twentieth century as “Indian rubies.” But it was not until about the 1990s that any effort was made to mine the basalt for gem material on a large scale. This occurred on the San Carlos Indian Reservation, near the town of Peridot, in Gila County. For several years, there were vast quantities of peridot being extracted from the rock as a result of actual mining instead of just being collected from stream gravels and volcanic bombs on the surface. In Tucson at that time, dealers had barrels of crystal fragments, and cut stones in jewelry were being aggressively marketed via television sales. But within a period of a relatively few years, Arizona peridot seems to have virtually disappeared from the marketplace. It is not clear what caused this, but it has been suggested that rivalries within the tribal community may be responsible.

Figure 11. Faceted peridot (forsterite) from the deposit on the San Carlos Indian Reservation. Tino Hammid photo.

Figure 11. Faceted peridot (forsterite) from the deposit on the San Carlos Indian Reservation. Tino Hammid photo.

Turquoise

Turquoise was mined centuries before Columbus, some twenty-six hundred years ago, in what is today New Mexico. Pueblo Indians are known to have been mining turquoise in the Cerrillos area (about 22 miles southeast of Santa Fe) before Cortez landed in Mexico in 1519. Later, the Spaniards conquered the Pueblo Indians, who were reduced to mining turquoise as slaves until the mine collapsed, killing some twenty miners. This resulted in an uprising in which the Spaniards were driven out of New Mexico. The mine was then abandoned, and turquoise mining did not resume here or elsewhere in New Mexico until around the 1880s, and lasted until about 1910. Total production in New Mexico up to 1915 is said to have exceeded $5 million (Sinkankas 1959).

It was not until much later that active turquoise mining began in Arizona, mostly as a byproduct of porphyry-copper mines in the Globe-Miami district of Gila County, where veins up to 0.5 inch thick were discovered. There are numerous other occurrences in the state, but all have been rather sporadic producers of modest amounts. Around the middle of the last century, Nevada was the leading producer of turquoise in the United States, and appears to have regained that distinction as recently as the 1980s. There were mines all over the state, it seems, and these were being worked primarily for gem turquoise, rather than copper. It is reported that there have been more that one hundred different small mines and prospects operated for turquoise in Nevada since its discovery there.

Figure 12. The Sleeping Beauty copper mine, Globe, Gila County, Arizona, an important source of gem turquoise. Bob Jones photo.

Figure 12. The Sleeping Beauty copper mine, Globe, Gila County, Arizona, an important source of gem turquoise. Bob Jones photo.

Figure 13. Turquoise in matrix from Los Cerrillos, Santa Fe County, New Mexico, historically a valuable source of fine turquoise. Chip Clark photo.

Figure 13. Turquoise in matrix from Los Cerrillos, Santa Fe County, New Mexico, historically a valuable source of fine turquoise. Chip Clark photo.

Sunstone

Sunstone is a term that encompasses several different materials. In general, it is a transparent feldspar containing inclusions of another mineral, giving it a distinctive schiller (iridescence). Some of the best-known and most abundant sunstone has come from India. The inclusion responsible for the schiller in this material is hematite, which gives the material a rich, golden-orange color. Sunstone from the United States is limited to a half-dozen deposits in Oregon. Here the feldspar is labradorite, and the inclusions are copper. These gems are found in basalt flows some 8–10 feet thick, on average. The nature of the copper in the feldspar (i.e., the size of the dispersed particles) very much determines the amount of schiller and the intensity of the color, which can vary from a warm, rich red to pink and even green. Schiller occurs only when the copper crystals are large enough to reflect light. In some of this material, the copper is very easily seen.

There are currently five active mines in Lake County and another in Harney County, Oregon. At least one of the mines in Lake County boasts an average yearly production of some 50,000 carats of faceted stones, a large proportion of which are being cut into beads. The market for these gems appears strong, although briefly threatened recently by stones from Asia, described as andesine, which have been shown to have been produced through the artificial introduction of copper in a furnace.

Figure 14. An excellent piece of gem sunstone is found after screening at the Ponderosa mine, near Burns, Harney County, Oregeon. Joe Nagel photo.

Figure 14. An excellent piece of gem sunstone is found after screening at the Ponderosa mine, near Burns, Harney County, Oregeon. Joe Nagel photo.

Figure 15. Sunstone, labradorite colored by copper inclusions, from the Ponderosa mine, Oregon. This stone shows some of the rare green color as well. Tino Hammid photo.

Figure 15. Sunstone, labradorite colored by copper inclusions, from the Ponderosa mine, Oregon. This stone shows some of the rare green color as well. Tino Hammid photo.

Opal

Even though one almost always associates Australia with fine opal—and that country has indeed produced the vast majority of gems—the United States has its sources of lovely stones as well. Best known is that from Virgin Valley, Nevada. Described by Sinkankas (1959) as “incomparably beautiful in respect to play of color and unmatched in terms of size,” the opal from this deposit has a tendency to crack upon prolonged exposure, and merchants are understandably wary of it. Some is quite stable, however, and many museums display quite large pieces of pure opal, even if badly cracked. The opal here occurs in beds of volcanic ashes where it has replaced tree logs, limbs, and roots. Other deposits are found in many of the western states, particularly Oregon and Idaho, where it occurs in large transparent pieces that display flashes of rainbow colors when the light source is behind them; they are referred to as contra luz.

Figure 16. Contra luz opal from Opal Butte, Morrow County, Oregon; approximately 27 carats, cut by Kevin Lane Smith. Tino Hammid photo.

Figure 16. Contra luz opal from Opal Butte, Morrow County, Oregon; approximately 27 carats, cut by Kevin Lane Smith. Tino Hammid photo.

America's Own!

Depending upon one's definition of some gemstone names, this country can claim as many as five unique gem types, or as few as three. The copper-included sunstone from Oregon is by most standards found only in Oregon, although sunstone of other types is well known from several other countries. The copper-included feldspar now being mined somewhere in Asia, alluded to earlier, is seemingly bogus. The claim that hiddenite is uniquely American is also somewhat controversial. First discovered in 1879 in North Carolina and mined in 1880 by W. E. Hidden, after whom it is named, this variety of the mineral spodumene derives its lovely vibrant emerald-green to yellow-green color from the presence of measurable amounts of chromium. Much more recently, very large, pale green transparent crystals of spodumene have been found in Brazil; however, although the green color for these crystals has been attributed to traces of chromium, the color is not stable, and it will disappear with prolonged exposure to daylight. Thus, most authorities are unwilling to agree that this is hiddenite.

Figure 17. A magnificent gem hiddenite crystal from the Adams Farm mine, Hiddenite, Alexander County, North Carolina; 2.7 cm high. Irv Brown specimen, Jeff Scovil photo.

Figure 17. A magnificent gem hiddenite crystal from the Adams Farm mine, Hiddenite, Alexander County, North Carolina; 2.7 cm high. Irv Brown specimen, Jeff Scovil photo.

Figure 18. Fine crystals of benitoite on a matrix of white natrolite with a faceted benitoite from the Benitoite Gem mine, San Benito, County, California. Jeff Scovil photo.

Figure 18. Fine crystals of benitoite on a matrix of white natrolite with a faceted benitoite from the Benitoite Gem mine, San Benito, County, California. Jeff Scovil photo.

Figure 19. Three exceptional faceted benitoites from the Benitoite Gem mine. Paul Cory specimens, Jeff Scovil photo.

Figure 19. Three exceptional faceted benitoites from the Benitoite Gem mine. Paul Cory specimens, Jeff Scovil photo.

Legitimate U.S.-only gems do exist in the form of benitoite and red beryl, the latter sometimes referred to as bixbite, a poor name because of potential confusion with the mineral bixbyite, which is not related. Fortunately, the name is seldom used. Of late, some marketers of red beryl have proposed calling it red emerald—a terrible idea. Both of these gems enjoy the status of being regarded as rare, of very limited occurrence, yet quite lovely and highly desired both as mineral specimens and cut stones.

Figure 20. Red beryl, a fine large crystal from the Wah Wah Mountains, Beaver County, Utah. Bob Jones photo.

Figure 20. Red beryl, a fine large crystal from the Wah Wah Mountains, Beaver County, Utah. Bob Jones photo.

Figure 21. Red beryl from the Wah Wah Mountains, Beaver County, Utah. The cut stone weighs 1.19 carats and is in the Cornell University collection; the crystal is 1.7 cm and is in the Edward Arthur Metzger collection. Jeff Scovil photo.

Figure 21. Red beryl from the Wah Wah Mountains, Beaver County, Utah. The cut stone weighs 1.19 carats and is in the Cornell University collection; the crystal is 1.7 cm and is in the Edward Arthur Metzger collection. Jeff Scovil photo.

The mineral benitoite was first discovered in 1907 near Coalinga, San Benito County, California. The mineral, new to science at the time of discovery, was named benitoite because the deposit was located on the San Benito River. Despite its sapphire-blue color, benitoite was not widely accepted as a gem because it is relatively soft, 6–6.5 on the Mohs scale. Appropriately, however, benitoite is now the official California state gem.

When the property was first worked, the mine was known as the Dallas Gem mine, and it was in the interval between 1907 and 1911 that the 7.5-carat stone now residing in the Smithsonian's collection was found. It is estimated that from 1911 to 1967 some 1,500 carats were produced, most between 1952 and 1962. At some point in this part of its history, the mine was renamed the Benitoite Gem mine. The mine was worked during much of its history as a more or less part-time venture by its owners, and the production of faceted gems was appropriately modest until Collector's Edge took over the operation in 2001. The new owners processed the mine tailings and overburden for facet-quality pieces. They also mined fresh rock primarily for specimens until 2006 when they felt that they could no longer recover specimens of crystals on matrix, which was what held the greatest appeal to the miners. Today, the Benitoite Gem mine has a different owner who at times allows collectors to hunt crystals for a fee.

In terms of gem material, most of the production under Collector's Edge was in the form of small pieces that, when cut, were usually less than 1 carat in size, over 40,000 stones in all. Only about 200 stones over 1 carat were produced. The largest stone cut from this operation was a 10.87-carat round. A vast amount of uncut material remains, but although it might produce as many as 50,000 stones, they would all be less than 0.25 carat in size.

Benitoite has been found in at least two other countries, but it is exceedingly rare there and is not of gem quality.

As far as I know, red beryl is absolutely limited in occurrence to the United States. Some has been found in Sierra County, New Mexico, but the finest crystals and the best gem rough occur in Utah in two different places: the Wah Wah Mountains, Beaver County, and the Thomas Range, Juab County. In all three occurrences, red beryl crystals are found in rhyolite, a silica-rich, high-temperature igneous rock. The color is imparted by the presence of manganese. The crystals from the Violet 1 to 8 claims in the Wah Wah Mountains are superior to those from the Thomas Mountains, and these claims have produced the finest gem rough. Although the rough lends itself to the production of mostly very small stones, those 1 carat or more command prices equivalent to top emerald prices. It has been claimed that red beryl was found in these rocks as early as 1959, but it was not until about 1976 that red beryl specimens first appeared on the market (Sinkankas 1981).

Fire agate comes close to being a U.S.-only gem because it is only found associated with volcanic rocks in northern Mexico, as well as California and Arizona. Although technically not agate, the name fire agate is well established, and it may occupy a unique status among gemstones because it is truly a composite. The substrate is botryoidal silica upon which appears to have been deposited a thin film of iron oxide in the form of goethite. This film acts much like an oil slick on water, producing a variety of colors, usually very intense, due to thin film diffraction. This has then been blanketed by transparent chalcedony, thus protecting and preserving the delicate film while at the same time providing a window through which the underlying rainbow of vibrant colors can be seen. Today, fire agate is being mined commercially at only one site—Deer Creek, Gila County, in southeastern Arizona—and it is a minor, one-man effort (Jones, pers. comm., 2009). Not far from Deer Creek is another deposit, Slaughter Mountain, Graham County, that has produced outstanding pieces as well.

Figure 22. “Baby,” one of the many exceptional and named fire-agate gems from Slaughter Mountain, San Carlos Indian Reservation, Arizona; 21 carats. It was found by John Stevens and cut by Steve Marshall. Tino Hammid photo.

Figure 22. “Baby,” one of the many exceptional and named fire-agate gems from Slaughter Mountain, San Carlos Indian Reservation, Arizona; 21 carats. It was found by John Stevens and cut by Steve Marshall. Tino Hammid photo.

Rhodochrosite, as a faceted gem, has until very recently been limited in production to just one location, the Sweet Home mine, Park County, Colorado. This mine was worked for silver, beginning in 1873. A failure as a silver mine, the Sweet Home became world famous as a source of beautiful crystallized rhodochrosite specimens, actively producing specimens from the 1870s to the early 1890s. Most major museums in the United States and Europe have specimens in their collections from that era. Mining then ceased, and it was not until 1925 that the mine was worked again, this time with more success in the production of both silver and fine rhodochrosite specimens. Yet another unsuccessful effort to mine for silver occurred in 1966, but a rich pocket of crystals was discovered that produced some of the best specimens up to that point and “established the Sweet Home mine as the world's leading source of fine rhodochrosite” (Voynick 1998). Other attempts to mine for rhodochrosite followed, but it was not until Bryan Lees of Collector's Edge acquired the property and worked it in the 1990s that the most spectacular and prolific production of specimens was witnessed.

Figure 23. Rhodochrosite with tetrahedrite from the Sweet Home mine, Alma, Park County, Colorado. Daniel Trinchillo Jr. specimen, Jeff Scovil photo.

Figure 23. Rhodochrosite with tetrahedrite from the Sweet Home mine, Alma, Park County, Colorado. Daniel Trinchillo Jr. specimen, Jeff Scovil photo.

Figure 24. A selection of faceted rhodochrosite from the Sweet Home mine, Park County, Colorado, some set in jewelry. Jeff Scovil photo.

Figure 24. A selection of faceted rhodochrosite from the Sweet Home mine, Park County, Colorado, some set in jewelry. Jeff Scovil photo.

Until Lees' entry into the picture, very little attention was given to the gem potential of the rhodochrosite. Obviously, there were large amounts of broken crystal pieces, and much of this was seen to be gem quality. Rhodochrosite is a very soft mineral, and it possesses perfect cleavage in three directions, so it had never been considered a viable raw material for gems. Lees teamed up with gem-cutter and marketer Paul Cory, and, as a result, it was found to be facetable. Quite a lot of this rhodochrosite ended up in beautiful jewelry, which found a ready market. Lovely gems well over 50 carats have been cut, but most were much smaller. Between 1992 and 2006 it is estimated that no more than 2,100 stones larger than 1 carat were cut in the United States, and perhaps another 3,500 were cut overseas. Most of the latter were under 1.5 carats. Much of the inferior, more included, pieces ended up as cabochons, eggs, spheres, and six-sided rhombs in the shape of the crystals, thousands in all. The largest stone cut was a 92+-carat near-clean, cushion-shaped gem. Lees finally gave up mining the property in 2004, and it is highly unlikely that further mining will ever occur there. In the meantime, the status of the Sweet Home mine as the only important source of beautiful gem rhodochrosite has recently been challenged. Gem-quality rhodochrosite is now being mined in China, and its potential to out-produce the Sweet Home as a source of gem rough has yet to be determined.

There are many other occurrences in this country of various gems not included in this overview, either because the amount of gem material produced was very modest or the quality was inferior when compared with more famous occurrences elsewhere in the world. Among these are beryls from Connecticut and Idaho, as well as the variety morganite from California; garnets and jade from many different places; agates and jaspers; several feldspars; and rose quartz. Special mention should be made of the spodumene variety kunzite that was found in relative abundance as superb crystals in the pegmatites of San Diego County, southern California. Named after the famous American gemologist George F. Kunz, “the best gem spodumene in the world comes from this area” (Sinkankas 1959), although it has been surpassed in quantity and crystal size by more recent finds in Brazil and Afghanistan. Small amounts have been produced at several mines in San Diego County since its discovery in 1902.

Figure 25. Nephrite jade from Trinity County, California; 5.1 cm high. Jeff Scovil photo.

Figure 25. Nephrite jade from Trinity County, California; 5.1 cm high. Jeff Scovil photo.

It should be emphasized that the vast majority of the gem mining operations in the United States are small scale and subject to sudden closings and changes of ownership. For this reason, available information at the time of writing this article may not be valid by the time the article appears in print. I have done my best to obtain up-to-date details for the most significant workings, but I cannot guarantee that some things have not changed recently.

Acknowledgments

Many have generously contributed to this article including Bob Jones, Paul Cory, Pat Gray, Pete Modreski, Wendell Wilson, Chip Clark, and, especially, the late Joe Nagel, Jeff Scovil, and Tino Hammid who supplied most of the fine photographs. John Rakovan and Bob Cook assisted by improving the text, and I am greatly indebted to them.

REFERENCES

1. Sinkankas, J. (1959) Gemstones of North America, D. Van Nostrand Co, New York.

2. Sinkankas, J. (1981) Emerald and other beryls, Chilton Book Co, Radnor, PA.

3. Voynick, S. (1998) The Sweet Home Mine 1873–1989. Mineralogical Record 29:4, pp. 11-20.

4. White, J. S. and Cook, R. B. (1990) Amethyst occurrences of the eastern United States. Mineralogical Record 21:3, pp. 203-13.

John S. White, a consulting editor of Rocks & Minerals, operates Kustos, a museum/collector consulting business. Now retired, he is the former curator-in-charge of the National Mineral and Gem Collection at the Smithsonian Institution.

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