This is a pale to clear green variety of andradite garnet, regarded as being comparable in luster to diamond; hence the name, attributed to it in the latter half of the nineteenth century.
Appearance The color varies from a cold, very pale green (almost colorless with a green wash), to a mid or strong green, not as a rule a very lively color and similar to certain shades of green in tourmaline, zircon, or olivine. It often has good transparency and exceptional luster. Inclusions in the form of fine, curved fibers of asbestos are frequent and characteristic. These stones are usually given round, mixed, and brilliant cuts; more rarely, square or rectangular, step cuts. They are normally small. Specimens of more than one carat are uncommon, and those of several carats are extremely rare. Due to weakening inclusions the facets and edges are easily damaged with use.
Distinctive features The greenish color combined with strong luster, single refraction, and possibly asbestos fiber inclusions, are quite characteristic. However, the physical properties have to be measured to distinguish it from green grossular, green YAG, and occasionally from certain green zircons‘ with weak birefringence. -
Occurrence It is found mainly in the Soviet Union.
Value Because of its attractive appearance, color (paricularly when a lively, mid-green), and exceptional luster’. plus its rarity, it is one of the most valuable secondary gems.
Simulants and synthetics Green YAG, an artificial substance with the structure of garnet, is very similar and has been used to imitate both demantoid and green grossular. For the time being, at any rate, synthetic demantoid is not produced.