Demantoid is one variety of many from the garnet group of gemstones, garnets being most widely recognized in their deep red form. Demantoid garnets, however, are marked by a distinctive intense green to yellow-green hue, caused by the presence of the element chromium in its chemical makeup.
In addition there are three other types of green garnets--uvarovite, tsavorite, and grossularite-andradite--though demantoid garnets have two properties which make them special not only among the green garnets, but among all gems. The first is its strong fire, also known as dispersion, or the splitting of light into its individual spectral colours. Demantoid garnets are one of the few gems which posses this property to such a great extent—even more than in diamonds—emanating a rainbow of colours from within a deep green body. In fact, the name derives from the Flemish word ‘demant’ meaning diamond, due to its diamond-like lustre and dispersion. The other unusual feature, one that is completely unique, found only in demantoid garnets, are what are called ‘horsetail’ inclusions. Not found in every specimen, this distinctive internal feature is composed of curved needle-like tubular crystals radiating from a single point, resembling a horse’s tail.
Demantoid garnets also have a distinctive and interesting history. Though some varieties of garnets have been known since antiquity, demantoids were only discovered in 1853, in the Ural Mountains of Russia. It quickly became a coveted gem, first in Russia within the court of Tsar Nicholas I, and then spreading in popularity to Europe and America. The eminent Russian court jeweller Peter Carl Fabergé used the stone in many of his imperial commissions, as did prominent jewellers such as Tiffany and Boucheron. After the Russian revolution the stone fell from fashion, mainly due to a cessation of mining the gem in the newly established USSR. Due to the fall of the Soviet system in the early 1990s, coupled with the discovery of other sources of the stone, the most significant in Namibia in 1996, demantoid garnets, though still extremely rare, are experiencing a renaissance of appreciation. They make a unique gift for anyone with a January birthday, for which garnet is the birthstone.