GemNotes

A Wrap-Up of the Most Popular Gems

The Tucson gem shows in February produced more news than we could fit in last month’s issue. Here we wrap up our coverage with garnets, emeralds from Madagascar, “diffusion”-treated green topaz, and created emerald obsidianite. Also included are highlights of a panel discussion of gem lab directors regarding enhancements.

Enhancements

Emerald enhancements were at the top of many people’s list of concerns at Tucson. The world’s leading gem labs are now identifying and disclosing emerald enhancements in a similar manner, following a meeting last summer among nine of the top European labs, according to Robert Kane, former director of the Gübelin lab.

At an American Gem Trade Association seminar, enhancements and disclosure were the topics of a special panel of seven gem laboratory directors. For the first time, all the lab representatives agreed that “full disclosure” was important and that laboratories should be consistent with each other.

However, testing methods and identification reports still differ considerably. Some smaller labs rely only on “color flash” and the observation of surface openings to determine whether an emerald has been enhanced. These labs use nonspecific disclosure statements such as “usually seen” and generic stability statements like “may be unstable” because they cannot or will not identify the enhancement material.

At the opposite end of the spectrum is SSEF, the Swiss Gemmological Institute’s laboratory, which claims to identify all fillers and their extent, using FTIR infrared spectroscopy or, when necessary, Raman spectroscopy. Artificial resins and synthetic oils are identified on the report.

Tom Moses and Dr. Mary Johnson from the Gemological Institute of America’s Gem Trade Laboratory said GTL will soon be identifying the extent of the enhancement through visual observation. No identification of the filler or its stability will be reported. GIA’s research department is working on a study of the stability of all known emerald enhancements. GIA researchers have no intention of determining which enhancement is better than another.

While some labs have the equipment necessary to identify the filler, American Gemological Laboratories director Cap Beesley uses local university equipment to confirm AGL’s visual identification techniques and studies. Claiming to be a “buyers’ lab,” AGL discloses the type, extent, and clarity grade of each emerald tested. AGL’s term “Opticon-type,” which has spurred debate over semantics, simply refers to any synthetic epoxy-resin. Opticon is merely the most recognizable name.

Beesley took the brunt of arguments when he recommended that enhancement be removed if it can’t be identified, as some emeralds have undergone several different enhancements. If a customer would like the emerald re-enhanced, he suggested, one identifiable enhancement of the client’s choice could be used.

Finally, it’s widely known that the Brazilian emerald trade uses Opticon. Beesley announced that the Brazilians are also using Opticon to enhance tourmalines.

Created Gems: Emerald Obsidianite

This green gem made it onto the list of interesting gem names, alongside the usual Tucson fare of “Diamonique” (CZ), “tavolite” (a metallic oxide-coated topaz or CZ), and “tanavite” (a synthetic sapphire tanzanite simulant). Emerald obsidianite is neither emerald nor obsidian (natural glass) but a created green glass made from “rock dust” (“not ash,” say the distributors) from Mount St. Helens. The gem is distributed by Emerald Fox in Seattle and Leavenworth, Wash.

Emerald obsidianite is made from “rock dust” from Mount St. Helens.

Improved Tsavorite Supply

This bright, saturated African green garnet is a beautiful gem but has little following in the United States. That may be about to change. Kenyan explorer Campbell Bridges, who discovered tsavorite in 1972, has increased production and teamed up with Dana Schorr of Schorr Marketing in Santa Barbara, Calif., to distribute small calibrated goods and important larger solitaires. They hope to maintain consistent production and make more gems available for the retailer. Lack of supply was a persistent problem in the past.

“We’ve now got heavy mining equipment at the mines for the first time,” says Schorr. The mines are located 250 miles east of Nairobi near the Tsavo National Park region of southeastern Kenya. “There’s extensive inventory now, especially from 4 mm and down, in marquises, rounds, ovals, princesses, and trillions, in five color ranges and three clarity options.”

Bridges notes that “quite a few good pockets” recently have been pulled out of the new mines. The gems generally are small, yielding few finished gems larger than 2 cts. But the clarity and color make up for their small size. The colors range from dark to light, in strong to vivid saturated green, and in some instances bluish-green. This is somewhat different from the typically yellowish-green colors found in Tanzania.

Grape from India

Still selling well again this year as “grape” garnets are the medium-dark, very slightly reddish-purple to straight purple pyrope-almandines (“rhodolites”) from the Orissa region in northwestern India. The “grapes” are being promoted and trademarked by Columbia Gem House of Vancouver, Wash. And although the term “grape” is used internationally to describe almost any color of rhodolite, Columbia hopes to dispel this confusion.

Rhodolite is a rhododendron-colored garnet first discovered in North Carolina in 1898. Its colors range from light pinkish and dark reddish to straight purples. The grape color of garnet remains popular but has competition from the light pinkish-purple “raspberry” rhodolites from Africa.

Another atypically colored garnet maintaining its recently acquired popularity is the pure orange “mandarin” spessartite from Namibia. All three of these garnets—the grapes, raspberries, and mandarins—make excellent alternatives to the traditional brownish-red almandite birthstone. Of course, almandites are abundant and inexpensive at only $5 to $15 per carat. Typical prices for 6-mm round grape garnets are $50 to $75 per carat, raspberries $40 to $60 per carat, and mandarins $150 to $200 per carat.

Demantoids Still Available

Sergey Basakov from Disten Ltd. in Moscow showed demantoids from the original mines discovered in the late 1860s as well as new Russian sites. Several dozen other dealers in Tucson were also displaying demantoids. Bill Larson from Pala International in Fallbrook, Calif., had what was probably the most complete collection.

Basakov conveyed an impressive knowledge of the material as he proudly showed his more expensive medium-saturated, slightly yellowish-green demantoids. This color allows the gem to exhibit the most obvious diamond-like dispersion, or “fire.” Demantoid, after all, is best known for this property. Demantoid can come in a range of tones and saturation. While the very popular deep green emerald-like demantoids have a spectacular color, the rich saturation masks the “fire” and thus diminishes its value.

For the gemologists in the Tucson crowd, both Larson and Basakov had hidden away a few special demantoids displaying the central “horsetail” inclusions, the radiating fibers of bysolite-chrysotile that are unique to this gem. Demantoid is one of the few gems that becomes more valuable as the inclusion becomes more evident. Sales were slow with retailers but reportedly brisk among dealers.

Green Topaz

Green was a popular color at nearly all the shows. Making green much more affordable this year was Leslie & Co. of San Francisco, supplying what it calls “diffusion”-treated green topaz.

“Diffusion”-treated topaz first appeared at last year’s Gem and Jewelry Exchange (GJX) tent show, displayed by Jacoby Gems. Those gems appeared very thinly coated and were quite brittle. This year’s supply was a slightly better-looking material.

Beginning with the colorless and faceted natural topaz, the gem is cooked in a chemical bath, which reportedly allows the topaz to take up a thin layer of color-inducing elements. Leslie claims that the gems are resistant to heat (up to 3,000°F), steam, and ultrasonic cleaning. The company will replace any damaged gem for free. Single 6.5-mm round brilliants sold for about $40. Other manufacturers of “diffusion”-treated topaz showed very thin and spotty color with numerous areas of chipping.

Emeralds from Madagascar

A five-year-old deposit of gem-quality emerald in Madagascar is now being considered for commercial mining, says N. Zavarhoussen, a specialist in gem minerals from SOMIDI, Societe Mining Discovery, in Antananarivo, Madagascar. On display at Tucson were a small number of gem-quality emeralds in strong African-saturated color and good commercial clarity. There was also an enormous mineral specimen weighing 76 kg and showing more than 100 large, well-defined emerald crystals. Look for these to be readily available sometime next year.