Demantoid is the green-colored variety of andradite garnet. Discovered in Russia in the early 19th century, demantoid was identified as a variety of andradite in 1849 by noted mineralogist Nils Gustaf Nordenskiöld. Russia was long the only source of this rarest of garnets. Supply was so low, demantoids were usually seen only on antique jewelry pieces. Since the 1990s, new sources have been discovered, and the gem remains a desirable, but very expensive, jewelry stone.
Even with new sources, demantoid remains very rare. Clean, facetable stones command very high prices per carat. Faceted stones greater than 1 carat are rarely seen.
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
|Is a Variety of||Andradite|
|Colors||Yellow-green, green, deep green|
|Specific Gravity||3.82-3.88 (San Benito, CA demantoid: 3.81)|
|Spectral||A strong band is visible at 4430, cutoff at the violet end of the spectrum. Chromium spectrum is visible, with a doublet at 7010, sharp line at 6930, and two bands in the orange at 6400 and 6220. Demantoid is red in the Chelsea filter.|
|Phenomena||Occasional chatoyancy due to byssolite inclusions.|
|Formula||Ca3Fe2Si3O12, chromium (Cr) traces cause green color, ferric iron (Fe3+) traces cause yellow color.|
|Etymology||After the old German demant for “diamond,” due to the stone's high dispersion.|
|Occurrence||Schists and serpentine rocks; metamorphosed limestones and contact zones.|
|Inclusions||Horsetail inclusions of byssolite (fibrous amphibole).|
The exceptional brilliance and dispersion of the demantoid inspired Nordenskiöld to name this stone “diamond-like.” Nevertheless, this garnet gem has greater brilliance and a higher dispersion than its diamond namesake. It’s also far more brilliant than other well-known green gemstones such as emerald, peridot, and fellow garnet tsavorite. The dispersion can be masked by dark body color, but small, light-colored gems are quite dazzling.
Demantoid was a popular gemstone during the Belle Époque period (1890-1915), especially in Art Nouveau jewelry. The Russian Czars particularly favored this gem.
Heat can be used to improve color. This is a stable and undetectable treatment.
- Russia: the Ural Mountains region; Koryakskoe plateau; Kola Peninsula.
- Namibia: a commercially important source since 1996.
- Madagascar: a commercially important source since 2009.
- Italy: Ala, Piedmont, a source of dark apple-green demantoids.
- United States: San Benito County, California, unusual cat’s eye material.
- Afghanistan; Azerbaijan, Canada; Iran; Pakistan; South Korea; Sri Lanka; Zaire.
Demantoids are typically small. Stones larger than 10 carats are very rare. The largest demantoid ever found hailed from the Russian Urals and weighed 252.5 carats or 50.5 grams.
Demantoids have been called “Siberian emeralds,” “Siberian chrysolites,” and “Ural chrysolites.” Of course, garnets are chemically and optically distinct from these gem species. Consult our article on false or misleading gemstone names for more examples from the garnet family.
Heat sensitive garnets should be cleaned with warm water, detergent, and a soft brush. Avoid mechanical cleaning and exposure to extreme heat. Consult our gemstone care guide and jewelry cleaning guide for more information.