GemNotes

Arizona Andradite Debuts

The past three years have witnessed numerous new garnet finds – transparent yellow-green grossular-andradites, or Mali garnets, from western Africa; the strongly saturated purple “grape” rhodolites and yellow-orange “fireball” spessartites from Madagascar; mandarins from Namibia; and “Kashmirines” from India and Pakistan.

Now we have yet another new garnet, the Arizona andradite. Charles Vargas of Apache Gems uncovered the andradites while mining peridot last year in the Apache territory near San Carlos, Ariz. Among the find were beautiful golden-yellows (sometimes called “topazolite”), greenish-yellows, and reddish-browns. The mines also have produced a limited amount of fine-quality demantoids, the better-known variety of andradite garnet.

A lovely accent. Demantoid, a top seller in Tucson last February, owes its resurgent popularity to two important deposits in Namibia and Russia. Thanks to demantoid’s long history and fantastic fire, the slightly yellowish-green gem virtually sells itself. The non-varietal andradite, on the other hand, has won little recognition up to now.

Vargas intends to change that. He’s hoping that Los Angeles designer/manufacturer Andrew Sarosi will help promote Arizona andradite onto the salable list of gemstones. Since the mine so far has yielded only small gems, Sarosi has used them as side stones to accent larger gems.

Thanks to its dispersion – which, like demantoid, rates above diamond’s – andradite makes a terrific accent. Demantoid’s dispersion can be somewhat masked by chromium, which also accounts for its green color. The Russian material seen in Tucson had a high chromium content and very saturated green color, making it less dispersive than the Arizona gems. Arizona andradite is not overly saturated, which accounts for its high dispersion. The goldens, cognacs, and straw-colored andradites, which contain little or no chromium, are especially dispersive.

The Arizona mine includes two separate deposits of andradite and demantoid. One contains only trace chromium, the other higher amounts. The goldens show no detectable chromium, while vanadium and iron color the straw and light-green varieties.

Mining, cutting, and polishing. Mining andradite requires none of the heavy equipment and explosives used to extract the neighboring peridot, lying 50 feet under hardened lava flow. Hidden just beneath the surface, andradite is mined solely by hand.

Processing demantoids and other andradites requires diamond-like standards for angles and proportions. It calls for accurate lapidary equipment and “meet-point” faceting expertise. At 6 1/2 on the Mohs scale, andradite is softer than quartz, so it takes more effort to achieve an adequate polish.

Fancy Lists Still Getting a Bum Rap

The Rapaport Diamond Reports’ wholesale price lists for emerald and marquise shapes are rarely used by the wholesale trade. But that hasn’t stopped Martin Rapaport from publishing them even after two years of widespread neglect. He considers the lists a valuable service for retailers and appraisers who cannot quickly calculate emerald cut prices from the pear-shape list.

So why has the trade rejected the two new lists? Rapaport – who admits that even he doesn’t use them when buying and selling diamonds – says it’s just a matter of convenience. “It’s too confusing,” he says. “Most dealers don’t want a bunch of lists hanging around.”

But that’s not quite the whole story. When the first marquise and emerald lists came out, Rapaport used the “full discount” for emerald cuts. (“Full discount” refers to the fact that most diamonds actually trade for 30% to 35% below the list prices.) So in reality, he printed the legitimate prices at which diamonds were being traded.

Of course, dealers staged a fit. They said Rap’s prices were far too low and did not accurately reflect the market. “Everyone freaked out,” Rapaport says.

“The marquise list was a little profitable, but the emerald list was not,” says manufacturer Meyer Herz. Fancy dealer Allen Dubinsky remembers that “it was like the movie Network. We were mad as hell and not going to take it anymore.” Rapaport immediately revised the emerald list, boosting prices by as much as 20%.

Just how accurate are the emerald and marquise price lists today? Most dealers say they really don’t know, since they haven’t looked at them in months. Instead, most dealers calculate fancy prices using the pear-shape list, which comes with percentage conversions for the other fancy shapes. (For example, emerald cuts may trade 5% to 10% below pears, while marquises may bring a 5% premium.) Dealers have been using the pear-shape list in this way for at least a decade.

Rapaport says he doesn’t mind that the emerald and marquise lists aren’t widely used. Other dealers are more blunt. “It gives you a little more open space, a little more room to play with,” says dealer Bruce Smith. “If there were a marquise list, you would have to calculate everything down to the last penny. There would be no room for profit.”

Some dealers even think that selling princesses and Radiants is currently in vogue partly because there is no established list. “The reason people are pushing princesses and Radiants is because there is profit in them, and the reason there is profit is because you are dealing with the pear list,” says Herz.

The ongoing controversy over the emerald and marquise lists shows just how powerful the Rap sheet has become. Some think it’s too powerful. For Rapaport, the charge that his new fancy lists could hurt industry profits has a familiar ring. For 20 years, he has argued that his lists do not hurt industry profits, and for almost that long many dealers have blamed them anyway.

Now that the diamond market is hurting and prices are starting to fluctuate, the “Rap sheet” has again become a lighting rod. At the recent World Diamond Congress in Bangkok, Rapaport’s lists were a major discussion topic for the first time in years. Even De Beers executives privately blame the list as one reason for the industry’s sagging profits.

Rapaport counters that his list simply reflects the market, and that he has become the scapegoat for bad economic news. “People say, ‘Oh no! Rapaport’s prices went down,’ ” he says. “They don’t mention that the Japanese economy just died. Market forces are driven by supply and demand. Price information is important, but it doesn’t affect the market. It’s like blaming the weatherman for the weather.” – Rob Bates

DECEMBER’S Birthstones: Turquoise and Zircon

Compared with the rest of the year’s durable and popular birthstones, December’s gems might seem like curious choices. Turquoise is the only birthstone that’s opaque. And owing to its heat-treated color enhancement, blue zircon is quite brittle. Even so, the historical significance of turquoise and the diamond-like qualities of zircon are fascinating. The facts and folklore of these birthstones will be of interest to customers born in the last month of the year.

Turquoise

History. The tale of turquoise dates back to Egypt’s first dynasty, circa 3000 b.c. Turquoise mined in the Maghara valley of the Sinai Peninsula was used to make fine jewelry and ornaments. Often combined with lapis and carved as scarabs, turquoise was worn exclusively by priests and nobility, most notably King Tutankhamen (1370-1352 b.c.).

Most Americans associate this birthstone with Native American silver jewelry. Turquoise played an important part in American life dating back to 700 b.c. The Anasazis and Hohokams were the first North Americans to mine turquoise in New Mexico, Arizona, Utah, and Colorado. Turquoise was used not only for fashion and talismans but also as an item for trade; it may well be America’s first currency. Native Americans considered turquoise a symbol of wealth and good fortune and believed it protected against danger and illness. Pre-Columbian Indians in Central America and Mexico crafted turquoise beads and pendants as far back as 500 b.c.

Of course, the world’s finest turquoise, Persian, is mined in Iran. Writings from the 12th century b.c. indicate that Isaac, son of Abraham, opened mines at Neyshabur in the mountainous northeast. Many are abandoned today, but some are still in operation and are known as the Isaac mines. Turquoise became a major currency for ancient Persians and was traded as far east as Siberia.

Turquoise was a desirable gem in other ancient sites. Tibet, Mongolia, and China had tur-quoise deposits. Chinese turquoise dates back to 1200 a.d. It’s inferior in quality to Persian turquoise and so was used mainly for carvings and for decorative art.

After invading China in the 1800s, the British brought turquoise back to England. The gem became fashionable in Europe during the reign of Queen Victoria (1837-1901). Victorian and art nouveau jewelry was commonly set with large Persian turquoises, emeralds, and garnets.

Quality. Two varieties of turquoise are equally prized for their beauty. The historical preference, and the one still favored in the Middle East and Europe, is for gems that show a pure, continuous, “robin’s egg” blue. Then there are those, mainly in the Western Hemisphere, who prefer an evenly spread black veining similar to a spiderweb. Persian turquoise is best known for its pure, even color, while that from Bisbee, Ariz., yields a perfect spiderweb matrix. In fact, every mine can produce a variety of qualities.

The quality of turquoise depends on three criteria: luster, color, and matrix.

  • Luster. This reflects how well the gem has been polished. A fine-quality gem accepts polishing and displays a bright, smooth, and shining finish. A poor-quality gem will show pits, polish lines, and a dull finish. Polish and luster are affected by the hardness and density of the material. Turquoise varies in hardness (from 2 to almost 6 on the Mohs scale) and density (from 2.6 to 2.9). Fine-quality turquoise is characterized by high density and hardness, allowing for a better polish.

  • Color. The color of turquoise can range from green to blue, depending on its chemistry and porosity. Turquoise in its pure state is a copper aluminum phosphate. The more copper, the more blue the turquoise. Adding iron lends turquoise a greenish hue. A purer, high-density material typically shows a medium-saturated blue. U.S. deposits of fine-quality blue gems include those at Bisbee and Morenci, both in Arizona. High-quality, green-hued turquoises come from Chinese mines, especially the Skyhorse and China Mountain mines, as well as U.S. finds at Cerillos, N.M., and Fox, Ariz.
    Lesser-quality turquoise with greater porosity can change to a greenish-blue color owing to impurities entering into the gem. This can happen while still in situ as groundwater containing other elements – iron oxide, for example – seep into the turquoise. Skin oils, perfumes, soapy water, and even silver polish will commonly cause turquoise to change color after years of wear.

  • Matrix. Matrix is simply the host rock in which turquoise is formed. Persian turquoise is commonly cut and fashioned without any host material. In U.S. and Chinese deposits, it’s more common to find the host rock intertwined with turquoise. In these gems, it’s preferable to have an evenly distributed matrix, an appearance known as spiderwebbing. The desirability of matrix is a matter of personal taste.

A fine-quality, black spiderweb matrix is characteristic of the Lone Mountain, Skyhorse, and China Mountain mines. Thick brown and black matrix is typical of Bisbee, considered by many to be the finest of the matrix variety. Morenci turquoise contains spiderweb and patterned matrix along with pyrite, or “fool’s gold.”

Enhancements. Natural turquoise is mined, cut, and polished with no further enhancements. Gemstones processed in this manner are typically of very fine quality.

Turquoise also can be artificially enhanced. For centuries, immersing turquoise in animal fat or vegetable oil gave the gem a “wet” look, making it more salable. Today, much of the commercial turquoise set in jewelry has been enhanced in one way or another. Enhancements are described in very specific terms, and subtle differences can affect value.

  • Stabilization. Common U.S. turquoise often occurs as a nugget that’s too porous or soft to hold a polish. Immersing it in a liquid stabilizer, most likely an epoxy resin or polystyrene, chemically hardens the stone. Stabilization does not alter the turquoise mineral itself but simply fills its pores. When the epoxy hardens, the gem can be cut, polished, faceted, and even drilled without the gem crumbling. The enhancement also protects the natural color by preventing chemicals from entering the pores.

  • Color stabilization. Color can be added to turquoise by mixing a dye within the stabilizer. Of course, color-stabilized turquoise has less value than gems appearing naturally with this color.

  • Reconstructed turquoise. This variety is a compressed blue block of pulverized turquoise and epoxy resins produced to look like the real thing. Reconstructed turquoise is inexpensive and easy to work with.

  • Imitations and synthetics. Turquoise imitations have been around for as long as the natural gem. There are celluloid, plastic, ceramic, and glass imitations. Also, natural gems such as howlite, magnesite, and calcite can be dyed to look like turquoise.

Synthetic turquoise is the real thing chemically but is manufactured in a laboratory. Synthetic “matrix” turquoise is easily identified by its unnatural, even matrix. The “Persian” replica, however, is difficult to identify, so you need to be careful when evaluating fine-quality material.

Processing turquoise. After the gem is mined, it’s washed and dried, then graded for size and color as well as its purity or matrix design. Those that are left natural are tumble-polished. Stones that are not left as nuggets are flattened and then backed with a powdered steel material for stability while polishing and setting. After the backing is complete, the stone is polished and dried for a few days until it shows its true color.

Care and cleaning. Natural turquoise is porous and can be damaged by perspiration, oils, cosmetics, and perfumes. Preferably, it should not be worn against the skin. Turquoise can also change color with overexposure to light and heat. The loss of water gives the stone a greenish hue.

A turquoise ring should be removed before hand-washing. If the gem needs to be cleaned, do so with warm, soapy water.

Prices. In ancient times, turquoise was valued more than gold. Today its value ranges from pennies to more than $50 per carat.

For the collector, cabochons from the now-closed Lander Mine in Nevada that have a deep blue color and a tiny black spiderweb matrix may have a retail value of $300 to $500 per stone. Exceptionally fine-quality cabochons from the Skyhorse mine in China could cost $50 per stone. Other Chinese turquoise of lesser quality can sell for as little as 30 cents a carat.

In the mid-range, a newly discovered deposit in New Mexico called the Lost Mine of Enchantment is expected to produce fine-quality gems that could sell for $3 to $15 a carat.

Zircon

History. Zircons have served as talismans as far back as the sixth century. Once it became possible to facet gems in the 14th century, heat-treated colorless zircons were passed off as diamonds. The change to a colorless appearance enhanced the gem’s brilliance. This, along with zircon’s natural dispersion, made it virtually impossible to distinguish rose-cut zircon from diamond. Found in ancient riverbeds known as gem gravels in Matara on the southernmost tip of Sri Lanka, zircons were considered inferior-quality diamond and were known as “Matara diamonds.”

Color. While blue zircon is the December birthstone, the gem also occurs in yellow, brown, green, orange, and red. Blue zircons, like the colorless variety, are created by heating natural reddish-brown stones to 1,000°C. Rarely does zircon occur naturally as blue.

Locations. Sri Lanka and Thailand historically have been the two major sources for zircon. The newer, more important deposits are in Cambodia. Africa, particularly the southern region, may dominate the zircon market within the next 10 years.

Radioactivity. Zircon is a zirconium silicate containing trace elements of uranium and thorium. That makes the gem mildly radioactive. In fact, some green zircons can register radioactivity on a Geiger counter, yet many people still consider them wearable.

The older the zircon, the more the radiation has damaged the crystal structure. That makes the gem fragile. Blue zircon’s heat treatment also breaks down the crystal structure, leaving the gem brittle and easily scratched and chipped.

Prices. In 3- to 5-ct. sizes of fine quality, zircon sells wholesale for $30 to $50 per carat for colors other than blue. Blue stones can run $45 to $90 per carat.

Astrological gems. If you were born between Nov. 21 and Dec. 20, you’re a Sagittarius and can wear November’s gem, topaz. If you’re a Capricorn, born between Dec. 21 and Jan. 20, your astrological gem is the ruby.