Demantoid Buying Guide
DEMANTOID GARNET
BUYING GUIDE
By Richard W. Hughes
Introduction/Name
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.
Color
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.
Lighting
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.
Clarity
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.”
A classic example of a horsetail inclusion in a Russian demantoid garnet. (Photo: Wimon Manorotkul)
Cut
In the market, demantoids are found mainly as round brilliant or cushion cuts. Cabochon-cut demantoids are not often seen.
Prices
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.
Stone Sizes
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.
Sources
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.
Another Ural pearl in matrix. (Photo: William Larson)
Enhancements
Some demantoid garnet is heat-treated to improve the color. The resulting stones are stable under normal wearing conditions.
Imitations
Demantoid garnet has never been synthesized, but a number of imitations exist. These include green glass and green YAG.
This suite of 0.75–2.0 ct. demantoid garnets shows the typical range of colors possible. The ideal body color would be the center stone, which is not too light or dark, but the lighter tones show off demantoid's fire to better effect. (Photo: Wimon Manorotkul; Gems: Pala International)
Properties of Demantoid Garnet
| Demantoid Garnet (a variety of andradite garnet) | |
| Composition | Ca3Fe2(SiO4)3 |
| Hardness (Mohs) | 6.5 to 7 |
| Specific Gravity | 3.84 |
| Refractive Index | 1.888; Singly refractive |
| Crystal System | Cubic |
| Colors | Light to deep green |
| Pleochroism | None |
| Dispersion | 0.057; this is among the highest of all gems, even higher than diamond |
| Phenomena | None |
| 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 |
| Synthetic available? | No |
Further reading
For more on Russia’s demantoid mines, see Gabrièl Mattice’s Gem Spectrum Newsletter, Vol. 4, No. 1.