The demantoid is a member of the garnet family, most widely recognized in their deep red form, and is actually a variety of the garnet mineral andradite. 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. To own a demantoid garnet is to have a truly rare gemstone, however they are one of the lesser known gems.
Demantoid garnets have two properties which make them special, not only among the green garnets, but amongst 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 possess this property to such a great extent, with a refractive index of 1.880 to 1.889, even higher than that of a diamond, 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 to demantoid garnets, are ‘horsetail’ inclusions. Whilst 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.
Most demantoid garnets are small in size, with large ones being extremely rare. Once cut, only a few stones weigh more than two carats, with most of them hardly exceed one carat. If you come across one set in a piece of jewellery, it is always likely to be a small stone.
Demantoid garnets also have a distinctive and interesting history. Though some varieties of garnets have been known since antiquity, demantoids were only discovered in the mid-19th century, 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 being 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.
The demantoid garnet has long been prized for its rarity and brilliance, and remains today one of the most unusual stones available in jewellery in the world.
