One of the most valuable gemstones, Demantoid is the green variety of Andradite garnet. It’s name comes from Dutch, “demant”, meaning diamond, because it can exhibit fire like a diamond, and can be as green as the finest emeralds. It is believed that the colour comes from the presence of Chromium in the stone. Its fire is best seen in stones with less body-colour, so generally one chooses between fire or colour in a particular piece.
It was first discovered in the Ural mountain range in Russia in the 19th century, and very quickly became popular with jewellers like Fabergé and Tiffany’s. Russian Tsars were particularly fond of demantoid jewellery. Its scarcity forced it into near-obscurity during the 20th century, however the discovery of a large mine in Namibia in the 1990s brought it back into the public arena once again.
The Russian gems exhibit a wonderful inclusion, of radiating needles, called “horsetail” due to the similarity with a sweeping tail of a horse, which is absent from the Namibian stones. This is a very unusual case where an inclusion makes a gemstone more valuable!
Examples are usually small, typically under 1 carat.