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Demantoid Garnet from Namibia
Since the deep red garnets are abundant and inexpensive, garnet has been regarded by some buyers as a rather common gemstone. Yet, while there are some common and inexpensive garnets such as almandine, there are also some rare and expensive ones. The rarer garnets include spessartite, tsavorite and demantoid.
Of these rare garnets, demantoid is by far the rarest and most valuable. In fact demantoid is one of the rarest of all colored gemstones. Particularly fine demantoids can command thousands of dollars per carat.
What makes demantoid garnet so special? Demantoid belongs to the andradite variety of garnet, which is calcium iron silicate with a density of 3.7 to 4.1 and a refractive index of 1.88 to 1.94. The high refractive index makes demantoid the most brilliant of all the garnets, and demantoid garnet has a higher refractive index than sapphire and ruby. In fact, the refractive index of demantoid is in the same range as zircon and sphene.
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). Indeed, the very name demantoid means "diamond-like luster".
While most garnet varieties have been known since ancient times, demantoid garnet was not discovered until 1853, in the Ural Mountains of Russia. The Russian deposits remained the only source for demantoid until a major find in Namibia in 1996. The Russian demantoid is rarer and is generally more highly valued. Distinctive 'horsetail' inclusions are the telltale sign of Russian demantoid, since to date, these inclusions have not been found in the Namibian material. But the Nambian demantoid deposits have made this gemstone available to a wider market at a more affordable price.
Spinel is best known for its ruby-like color. Some of the most famous gems thought to be rubies are actually spinel. For more detail on this topic please read our article on rare spinel.
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Happy gem hunting,Your friends at GemSelect