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Cambodian blue zircon

Jewel of the Month
By Gary Roskin, G.G., FGA, Senior Editor
This story appears in the September 2003 issue of JCK magazine
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Rough crystals of blue zircon, like the ones at the top of the opposite page, are becoming more available, according to Mike Williams, Loveland, Colo. The three free-form carved gem blue zircons—6.57 cts., 4.43 cts., and 5.68 cts.—were carved by Sherris Cottier Shank, a carver and sculptor from Southfield, Mich., and a member of Gem Artists of North America (GANA). "The top of the gem is carved in a curved linear motif, and the pavilion is carved to reflect maximum light," notes Shank. "My aim always is to produce a gem carving with fluid elegance that is also bright and happy." Rounding off the display are two traditionally faceted brilliants, one round and one oval. For more information about Shank's work, call (888) 580-9971, e-mail: gemscapes@aol.com, or log onto the GANA members gallery at www.Gemartists.org.

Sometimes, a gemstone's origin really does make a difference. Such is the case for zircon from Cambodia. Unlike zircon found elsewhere, heat treatment transforms this material into a vivid blue gem.

History and lore. For more than a thousand years, zircons have been recovered from the alluvial gem gravels of Sri Lanka. But it wasn't until the late 18th century that a professor of chemistry from the University of Berlin, M.H. Klaproth, named the gem "zircon." Klaproth, sometimes labeled "the father of physical chemistry," discovered the elements strontium, titanium, and chromium. In 1789 he named the element zirconium and the gem zircon. He derived the name from the Arabic words "zar" and "gon," meaning "gold color"—the color of most zircon samples at that time.

But it was colorless zircons that were sold in Indian bazaars as "Jargoons"—a corruption of "zar-gon." They also were sold, sometimes deceptively, as Matara Diamonds. Because of their high luster and strong brilliance, colorless zircons have been used for centuries as imitation diamonds. The zircon labeled Matara (sometimes spelled "Matura") Diamond is named after Matara, the largest city on the south coast of Sri Lanka. Matara was once considered the most important seaport for Sri Lanka's spice and gem trade.

Even though zircon is the modern December birthstone, it was more popular during the Victorian period than it is today. Colorless zircon was popular until diamond substitutes like YAG, GGG, and strontium titanate came into the market.

But don't let that deter you from promoting the magic of this gem. Zircon's mystical powers include protection from disease, pestilence, plague, contagious epidemics, poisons, injury, and thieves. The list also includes less miraculous achievements such as relief from insomnia and help with digestion.

Origin, color, and color enhancement. Zircons are found in Burma, Cambodia, Madagascar, Vietnam, and Sri Lanka as well as Australia, Canada, France, India, and Russia. Heated to create vivid blue stones, these unique zircons come only from the province of Ratanakiri (also spelled "Rattnak Kiri") in the extreme northeastern corner of Cambodia. Some dealers incorrectly pinpoint Pailin, the western border town noted for sapphire deposits, as the origin of the new blue zircons, probably because the Ratanakiri zircon is most likely transported through Pailin into Thailand for processing, cutting, and heat treatment.

Before heat treatment, Cambodian blue zircon is brown. Brown rough that doesn't treat to blue—or turns out ugly—is reheated, and yellows may result. Failing that, they will be heat treated again to turn them pure colorless. Yellows made from brown rough are unstable: They turn brown in sunlight and revert to yellow after a day in darkness.

"This material from Cambodia has been in plentiful supply since 2000 when a new deposit began producing," notes Mike Williams, House of Williams, in Loveland, Colo. "Not only was more material hitting the market, but the colors were generally darker than was previously available."

There also are brown zircons from the Thai/Cambodian (Pailin) border and from Vietnam, but both heat to a pale blue. There are rumors that Nigerian zircon also can be heated to make light blue stones, but the tons of brown zircon from Tanzania apparently will not turn blue at all.

Natural colors for zircon include colorless to pale yellow, or green. Heat-treated material can range in color from blue, green, dark red, yellow, cognac brown, orange, and colorless. The color is somewhat directional—i.e., usually stronger from one direction than another—but it tends to face up well no matter which direction you carve.

Quality. One should expect well-cut, eye-clean gems to be available and relatively inexpensive. Infamous for "paper wear" (abraded facet junctions caused by banging against each other in a parcel of loose stones), zircon has long been accused of being brittle. And for decades, this quality has been blamed on heat treatment. But because the enhancement is not considered a high-temperature treatment, many dealers suggest that zircon is naturally brittle. Whatever the cause, however, stones in parcels purchased in the Far East will be separated by individual "twists" of tissues.

Zircon is approximately one-third heavier than diamond. This means that zircon will appear smaller than a diamond—and most other gemstones, for that matter—of the same weight.

Simulants and imitations. Natural zircon has no synthetic counterpart. However, many still confuse it with synthetic cubic zirconia. Both colorless zircon and CZ have been used as diamond substitutes, but the two gem materials are gemologically unrelated.

Prices. As with most quality rough, smaller sizes are more available than larger ones. According to Mike Williams, "Rough up to 5 grams has been readily available with only a sporadic supply of rough in the 6- to 12-gram sizes." (Note: 1 gram = 5 carats.)

"Up until a few years ago, I'd never cut blue zircon," recalls gem artist Sherris Cottier Shank. Primarily, she says, that's because it wasn't available in sizes large enough to carve. "If I saw rough at all, it was available in one gram or less sizes. And since it's standard to have only 25%-30% recovery after carving, that would produce a finished stone in the 1-ct. or smaller range." And that's just not big enough for a carver, says Shank.

Accordingly, The Guide notes that 20-plus-ct. faceted gems are rare. Prices for 5-ct. to 10-ct. gems in the fine-quality category range from $75/ct.-150/ct. For gems under 5 cts., prices are in the $40/ct.-$80/ct. range.

Care and cleaning. With a hardness rating of 7, zircon is not soft—but it is brittle. Therefore, zircon-set jewelry should be kept separate from other gems and jewelry because of its potential for becoming abraded. "However, with reasonable care, blue zircon should give an owner little or no problems," notes Williams. "After all, if tanzanite and Mexican opals were used as ring stones, then blue zircon would certainly be a better choice from a durability standpoint." You can also include tourmalines and garnets in that category. Even so, zircon would probably be best suited for pendants instead of everyday rings.

Bench Care. "You don't want to put a torch to anything," says Philip Zahm of Philip Zahm Gemstones, Aptos, Calif. The heat from a torch can turn blue zircons into greens or grays. Some say you can repair color altered by heat by using a 100-watt light bulb, heating up the gem once again.

Ultrasonic cleaning should be okay, as long as the gem is not hitting another gem or piece of jewelry. "Be careful in bezel setting," advises Zahm. "And don't buy princess cuts."

Special thanks to Phil Zahm, Philip Zahm Gemstones, Aptos, Calif.; Mike Williams, Michael Williams, House of Williams, Loveland, Colo.; and Dick Hughes, Pala International, Fallbrook, Calif.

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