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• Demantoid Garnet from Namibia
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• Rare and Unusual Gems
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Demantoid Garnet from Namibia
Garnet has been a popular gem for many centuries, since it is a durable stone with very good brilliance. But because the deep red garnets are abundant and inexpensive, garnet has gained the popular reputation of being a rather common gem. It's an unfortunate misconception, since there are garnets which are among the finest of colored gemstones -- spessartite , tsavorite and demantoid.
Of these rarer garnets, demantoid is the rarest and most valuable. In fact demantoid is traditionally one of the rarest of all colored gemstones. Particularly fine demantoids can command prices of thousands of dollars per carat.
What makes demantoid garnet so special? Demantoid belongs to the andradite variety of garnet, which is a calcium iron silicate. It has the highest density (3.7-4.1) of any member of the garnet family, and an unusually high refractive index (1.88-1.94). The high refractive index makes demantoid the most brilliant of the garnets; and in fact demantoid has a higher refractive index than sapphire and ruby, and in the same range as zircon and sphene.
But demantoid's greatest claim to fame is its exceptional fire, the dispersion of white light into the colors of the spectrum. Demantoid has the highest dispersion rating (.057) of any jewelry gemstone, higher even than diamond (.044).
While most garnets have been known since ancient times, demantoid garnet was not discovered until 1853, in the Ural mountains in Russia. The Russian deposits remained the only source for demantoid until a major find in Namibia in 1996. The Russian demantoid is now very rare and expensive. Distinctive 'horsetail' inclusions are the telltale sign of Russian demantoid, since these inclusions are not found thus far in the Namibian material. But the Nambian demantoid deposits have made this gemstone available to a wider market and at a more affordable price.