Demantoid is a brilliant green variety garnet. It is considered to be the rarest and most valuable member of the garnet group of minerals. Demantoid has an exceptionally high refractive index making it not only the most brilliant garnet but also more brilliant than both ruby and sapphire. Demantoid garnet also has exceptional fire and boasts the highest dispersion rating of any jewelry gemstone available today, even exceeding that of fine diamond. Like most green garnets, it is typically found only in small sizes and specimens over 1-2 carats are very rare. In fact, demantoid garnet is traditionally considered to be one of the rarest colored gemstones today.
Demantoid garnet was first in discovered in 1853 in the Ural Mountains of Russia. Today, Russian demantoid is considered extremely rare and very valuable. Russian demantoid is highly prized for its distinctive golden 'horsetail' inclusions.