Demantoid

Demantoid is the emerald-green variety of andradite garnet. Its name comes from the old German word Demant, “diamond”, because it splits light even more strongly than diamond and gives fiery flashes. It was found in the mid-19th century in Russia’s Ural Mountains. It is usually small; stones over one carat are rare and it counts among the most valuable garnets.

Jewellery: Its emerald-green colour and diamond-like brilliance make it a gem for rings, brooches and earrings. Because hardness is 6.5–7, a protective setting is advised for rings; being sensitive to heat, it should not be cleaned in an ultrasonic cleaner. Collecting: Crystal groups in serpentinite and stones with horsetail inclusions are sought after by collectors.

It has a hardness of 6.5–7 on the Mohs scale. It scratches glass and steel; a steel knife cannot scratch it. Its specific gravity is 3.82–3.88 g/cm³.

Its best-known localities: Green Dragon mine, near Karibib, Erongo Region, Namibia; Antetezambato, Ambanja District, Diana Region, Madagascar; Bobrovka River (near Elizavetinskoye), Nizhny Tagil district, Ural Mountains, Russia; Valmalenco, Sondrio, Lombardy, Italy; Ala valley, Piedmont, Italy.

The green ranges from yellowish green to a vivid green close to emerald; some stones have a brownish tone that comes from iron. Its lustre is diamond-like (adamantine) and, because it splits light so strongly, it gives coloured “fire”; the green body colour can sometimes hide this effect. Russian demantoids often show golden, curving fibres radiating from a tiny chromite crystal, called “horsetail” inclusions. They are a classic clue to demantoid, but not every demantoid has them. Old trade names such as “Uralian emerald”, “Siberian emerald”, “Siberian chrysolite” and “olivine” are misleading; demantoid is a garnet, not an emerald or a peridot (olivine).

On the “street to diamond” value ladder it sits on step 7 of nine: Precious stone. Colour matters most for demantoid: intense green close to emerald is much sought after, while yellowish-green stones show more “fire”, so the choice is a matter of taste. Size has a large effect: most cut stones are under one carat, stones over two carats are rare and stones over three carats are very rare. Clarity, cut and origin also count; the “horsetail” inclusion, taken as a sign of Russian origin, is prized by collectors but is not proof of origin. Heat treatment may have been applied and should be disclosed.

Today crystal-therapy websites claim that demantoid brings vitality and renewal and attracts abundance and prosperity. The same circles say that demantoid supports the eyes, immune system and breathing, and that it protects travellers and lifts the spirits. Demantoid was found in the mid-19th century in the Urals, so there is no tradition of belief reaching back to ancient times. There is no scientific evidence that the stone brings vitality or abundance, supports the eyes, immunity or breathing, or protects travellers; someone with a health problem should see a doctor. This section reports beliefs; it is not health information. There is no scientific evidence for these claims and no stone replaces medical treatment.