BUYER’S GUIDE: ANDALUSITE

This is the eighth in a series by Senior Editor Robert Weldon designed to help jewelers buy different types of gems.

What to look for: A few decades ago, the mineral

andalusite, an aluminum silicate, was used to manufacture automobile spark plugs. Named for Andalucia, Spain, where it was first found, it held little promise as a gemstone. Indeed, gem connoisseurs scoffed at andalusite’s commonly small sizes, cleavage problems and often visible rutile needle inclusions.

But when andalusite was discovered in Sri Lanka and later in

Brazil, opinions began to change. The gems found there were quite dramatic and beautiful, especially if well-cut.

Andalusite has been largely a collector’s gem, partly for the reasons mentioned above, but also because it is relatively rare in consistent clean sizes and quantities. But its popularity among designers and jewelers who seek unique gems is growing.

A large andalusite (more than 5 carats) that is well-faceted (cut to show equal amounts of both pleochroic colors – mostly orange and green) is captivating. However, the colors often vary slightly from gem to gem. Some faceted andalusites may appear as only green, brown or yellow; these have simply not been oriented to exhibit the pleochroism at its best. Pink and violet andalusites also exist – though these are extremely rare, especially in larger sizes. Some green andalusites are heat-treated to change the color to pink. The treatment is rare and not detectable, particularly in clean gemstones.

Andalusites may appeal to the same type of customer who likes rare and/or unusual stones such as alexandrites. In fact, andalusites often have been labeled incorrectly “the poor-man’s alexandrite” (Alexandrite, a variety of the chrysoberyl species, is a change-of-color gem that appears reddish in incandescent light and green in daylight. See “Buyer’s Guide: Chrysoberyl,” JCK, September 1994, page 60.)

Chiastolite is an opaque variety of andalusite with an unusual, cruciform arrangement of carbonaceous inclusions. This gem often is cut en cabochon to isolate the cross-like pattern in the center. Cat’s-eye andalusites are formed by minute, fibrous, parallel rutile needles and are extremely rare.

Could be confused with: Andalusites can be confused easily with tourmalines, particularly golden to brown and some bicolor tourmalines. Some optical and physical properties overlap. The refractive index is 1.624-1.644 in tourmaline and 1.634-1.643 in andalusite; specific gravity is 3.06 in tourmaline and 3.17 in andalusite.

Tourmalines also are pleochroic, though not as strongly as andalusite.

Birefringence and the determination of visible pleochroic colors are key separators. Birefringence is .018-.040 in tourmaline and .007-.013 in andalusite. The Gemological Institute of America describes pleo chroism in transparent andalusites as a strong brown to yellowish green and brownish orange to brownish red. Other brownish and orangy gems – such as chrysoberyl, zircon and danburite – can be separated by their key gemological characteristics. The chiastolite form of andalusite can be identified visually, because no other gem material resembles it.

Enhancements: Though it is rare, some andalusites are heat-treated to modify and change their body color to a brownish-pink. People who regularly buy andalusite are more apt to want the classic orange to green.

Supply & price: Fine supplies of the material are available to steady customers and collectors, though not in large quantities. Main sources are Brazil, Sri Lanka, Russia, Africa and Madagascar.

Prices have risen dramatically. A decade ago, even fine larger stones were just a few dollars per carat. Now prices range from the mid-$60s to more than $100 per carat for exceptionally fine large gems (over 6 cts.). Chiastolite is less than $30 per stone and negotiable.

Gemology: Refractive index is 1.634-1.643, specific gravity is 3.17 and birefringence is .007-.013. Andalusite is 7-7.5 on Moh’s Hardness Scale.

Care: Andalusite has distinct cleavage, so take particular care when setting it. Warm, sudsy water combined with a fine-bristle toothbrush is best for cleaning andalusite jewelry. Avoid ultrasonic cleaners and steamers.

U.S. DIAMONDS MAY GO TO U.S. JEWELERS

Diamonds discovered near Kelsey Lake in Colorado may be marketed through U.S. retailers as an exclusive line of “American diamonds,” says Howard Coopersmith, president of Diamond Co. of Ft. Collins, Colo., a partner in the project.

The mine is expected to produce about 100,000 carats yearly when it goes into full production by 1997 or 1998, he says, and has an estimated life span of 10 years. What the deposit lacks in volume it recoups in quality: samples show that 65% of the diamonds are gem-quality, very white with relatively few inclusions. The average size is unavailable, but 25% have been more than 1 carat and several have been 6 to 14 carats, Coopersmith says.

His company is a junior partner to Redaurum of Toronto, which bought a controlling interest in the mine in December 1994. Redaurum, a public company traded on the Toronto Stock Exchange, also mines and markets production from the River Ranch Mine in Zimbabwe and a small deposit in South Africa. Redaurum sells the diamonds from those operations through tender offers in Antwerp.

No definite marketing plans have been made for the Colorado diamonds. But Coopersmith says several retail jewelry operations and U.S. diamond wholesalers have approached his company and Redaurum about marketing a uniquely American line of diamonds. “I believe we’ll be selling these goods separately,” he says.

Tender sales routinely bring prices 10%-15% over what De Beers’ Central Selling Organisation pays for comparable goods, he says. (Diamond consultants usually advise smaller producers to “ride on the backs of the CSO” because they can take the CSO’s stated 10% markup for themselves and avoid CSO-imposed charges for advertising and stockpiling.)

The Kelsey Lake deposit is actually a cluster of eight relatively small kimberlite pipes. Two of them contain diamonds in quantities that are economical to mine.

While most diamond mines are found in remote locations, the Kelsey Lake deposit is very close to Interstate 287 and fairly close to farms and ranches. But Coopersmith says the mine will cause no disruptions. “No ore or waste will be trucked from the site, and no chemicals will be used in processing,” he says. “Noise, dust and traffic will be minimal.”

ASIAN INSTITUTE MOVES TO NEW HOME

The Asian Institute of Gemological Sciences has moved into the new Jewelry Trade Center on Silom Road in Bangkok, Thailand.

AIGS relocated to be closer to the trade, which is concentrated in the trade center and elsewhere along Silom Road. The AIGS gemstone identification and research laboratory is on the sixth floor of the South Tower; the education facility and library are on the 11th floor.

AIGS, which recently upgraded its research and identification laboratory with state-of-the-art gemological equipment, provides identification, appraisal and origin reports on all gemstones. Its new address is AIGS, 919/1 Silom Road, Jewelry Trade Center, South Tower, 11th Fl., Bangrak, Bangkok, Thailand 10500; (66-2) 674-315-9, fax (66-2) 674-320.