Demantoid Buying Guide
Demantoid is the name given to the rich green variety of andradite garnet. The gem was first discovered in Russia and the name is derived from its diamond-like adamantine luster.
While the color of demantoid never equals that of the finest emerald, an emerald-green is the ideal. The color should be as intense as possible, without being overly dark or yellowish green. The color of demantoid is believed to be due to chromium. It should be noted that demantoid’s fire is best seen in the lighter, less saturate gems. Thus the color preference is a matter of individual taste. Some people will choose an intense body color and less fire, while others prefer a lighter body color and more fire.
Demantoid garnet generally looks best under daylight. Incandescent light makes it appear slightly more yellowish green. Because of its high dispersion, demantoid looks great in the same type of lighting as diamond, i.e., multi-point (as opposed to diffuse) lighting.
In terms of clarity, demantoid is relatively clean. Thus when buying one should expect eye-clean or near-eye-clean stones. Demantoids often contain radiating needle inclusions that are termed “horsetails.”
In the market, demantoids are found mainly as round brilliant or cushion cuts. Cabochon-cut demantoids are not often seen.
Demantoid is among the most expensive of all garnets, with prices similar to those fetched by fine tsavorite (the other green garnet). But like all gem materials, low-quality (i.e., non-gem quality) pieces may be available for a few dollars per carat. Such stones are generally not clean enough to facet. Prices for demantoid vary greatly according to size and quality. At the top retail end, they may reach as much as US$10,000 per carat.
Demantoid is rare in faceted stones above 2 cts. Fine demantoids above 5 carats can be considered world-class pieces. Most stones tend to be less than 1 ct.
The original locality for demantoid was in Russia’s Ural Mountains. Today, deposits of lesser material exist in Iran, Italy and Namibia, but the Russian material remains the standard by which the gem is judged.
Some demantoid garnet is heat-treated to improve the color. The resulting stones are stable under normal wearing conditions.
Demantoid garnet has never been synthesized, but a number of imitations exist. These include green glass and green YAG.
Properties of Demantoid Garnet
|Demantoid Garnet (a variety of andradite garnet)|
|Hardness (Mohs)||6.5 to 7|
|Refractive Index||1.888; Singly refractive|
|Colors||Light to deep green|
|Dispersion||0.057; this is among the highest of all gems, even higher than diamond|
|Handling||Ultrasonic: generally safe, but risky if the gem contains liquid inclusions
Steamer: not safe
The best way to care for demantoid garnet is to clean it with warm, soapy water. Avoid exposing it to heat or acids.
|Enhancements||Some demantoid is heat treated to improve the color|
For more on Russia’s demantoid mines, see Gabrièl Mattice’s Gem Spectrum Newsletter, Vol. 4, No. 1.