Professional Jeweler Archive: Bountiful Black

October 2001

Gemstones & Pearls/News

Bountiful Black

A new find of nephrite jade has uniform color, low prices and good timing

A source in Nevada is producing a black form of nephrite jade that draws raves from gem dealer Michael Randall of Gem Reflections of California. “It’s a homogenous, pure gem with few or no inclusions, it’s totally opaque and is just beautiful,” he says.

The material is well-suited for cutting as cabochons, though Randall says he will try faceting some material soon. Chunks as large as 44 pounds have been found. And because the material is so free from inclusions, gems can be cut to order. “It slices like bread and takes on a beautiful high luster when we polish it,” he says.

Because it’s abundant, large and relatively inexpensive ($2.50-$5 each for 12mm-by-10mm cabochons, $3-$6 each for 14mm-by-10mm cabs, according to The Guide, Northbrook, IL), some gem designers and cutters have bought large pieces to fashion into decorative sculptures.

Black, Not Basic

Nephrite jade, which belongs to the amphibole group, is a different mineral combination and has different optical and physical properties than jadeite jade. “Amphibole is the name of a mineral group in which members vary in chemistry and, hence, in some of their optical and physical properties,” say Cornelius Hurlbut and Robert Kammerling in their book Gemology, 2nd Edition (Wiley-Interscience Publication). Most green and dark green nephrite, for example, contains the minerals actinolite and tremolite. Gemologically, nephrite has a refractive index of 1.606-1.632 and a specific gravity of 2.95. While these characteristics can vary slightly, they help separate nephrite from jadeite.

Nephrite tends to be more fibrous and is tougher than jadeite. It can occur in light-to-dark green, yellow brown, white and gray. Black material tends to be mottled and irregular, which makes the Nevada find of homogenous color significant.

Nephrite is among the toughest gem materials, able to withstand above-average wear.

Randall says he forwarded some samples of the material to the American Gem Trade Association Gem Testing Center in New York City and is awaiting details of its findings.

Meanwhile, the material has undergone other testing, says Randall. “This black nephrite doesn’t appear to have any actinolite in it,” he says. That might account for its homogenous saturation.

Trend Time

Black nephrite could not have been found at a better time. Designers say the trend contrasting black and white gemstones (such as black and white diamonds) is increasingly popular. “Some manufacturers also look at it in terms of a replacement stone for dyed black chalcedony, which can turn quite brittle during the color treatment process,” says Randall.

• Gem Reflections of California, San Anselmo, CA; (800) 453-GEMS.

– by Robert Weldon, G.G.

Black nephrite from a new source in Nevada has entered the market. The material is a stark, uniform opaque black, and takes on a high polish. It’s an interesting alternative to dyed black chalcedony because of its toughness.

Photo by Robert Weldon.

Copyright © 2001 by Bond Communications