Demantoid Garnet

Demantoid is the green gem variety of andradite garnet, a calcium iron silicate. Its name derives from 'diamond-like,' a reference to its extraordinary dispersion, or fire, which actually exceeds that of diamond.

The green color comes from chromium (vivid green) or ferric iron (yellowish-green). First found in Russia's Ural Mountains in the 19th century, demantoid became a treasured gem of the Russian imperial era and remains one of the rarest and most coveted garnets.

Russian stones are famous for radiating fibrous 'horsetail' inclusions, considered a hallmark of origin and, unusually, often a value-adding feature rather than a flaw.

Demantoid forms in metamorphic and metasomatic settings, notably in serpentinized ultramafic rocks (as in the Russian Urals) and in contact-metamorphic skarns. Chromium-bearing host rocks supply the trace element responsible for the finest green color.

The characteristic horsetail inclusions in Russian material are fibrous chrysotile or byssolite that grew within the garnet, reflecting its serpentinite host. Skarn-type deposits, such as those in Namibia, generally lack horsetails and may show higher dispersion.

Key sources include the Ural Mountains of Russia, Namibia (Erongo/Green Dragon), Madagascar, Iran, and Italy. Russian and fine Namibian material is the most sought after.

Look for a transparent green to yellowish-green stone showing exceptional fire (rainbow flashes) that can exceed diamond. Hardness is 6.5-7, luster vitreous to adamantine, streak white, and the stone is singly refractive like all garnets.

The presence of golden, radiating horsetail inclusions is essentially diagnostic of demantoid (specifically Russian origin) and helps separate it from other green gems. High dispersion distinguishes it from tsavorite, which has little fire.

Versus emerald and green tourmaline, demantoid is isotropic (no pleochroism) and far more dispersive. Its high specific gravity and refractive index confirm the identification.

Demantoid is purely a gemstone, faceted for fine and antique-style jewelry where cutters orient stones to showcase its remarkable fire. It is a darling of collectors and high-end designers.

Because it is rare and seldom found in large sizes, demantoid commands high per-carat prices, with fine Russian horsetail stones among the most valuable of all garnets. Its moderate hardness suits earrings and pendants well, with care advised for rings.

Metaphysically it shares garnet's associations with vitality, prosperity, and renewal, though such claims are spiritual rather than scientific.