Demantoid

Demantoid is the green variety of andradite (Ca₃Fe₂(SiO₄)₃), coloured by chromium and iron, and is the rarest gemstone in the garnet group.

The name “demantoid” refers to its high dispersion, which, at 0.057, is higher than that of diamond.

The balance between dispersion (responsible for the so-called “fire”) and depth of colour (chromium content) is of great importance to the value of demantoids: if the colour is too deep (the chromium content too high), the dispersion is masked.

The first demantoids were found in 1855 in placer deposits of the Bobrovka River in the Ural Mountains.

The famous “horsetail inclusions”, prized by demantoid connoisseurs, bear witness to the formation of demantoids in serpentinised peridotites or serpentinites. They occur only in demantoids from certain deposits, particularly those in the Ural Mountains.