Alexandrite

ALEXANDRITE (EN: alexandrite; DE: Alexandrit; FR: alexandrite; ES: alejandrita; RU: александрит) is the mineral, rare transparent variety of the chrysoberyl of the different shades of the green colour in daylight, and of the purple or cherry-red one in the artificial light (which is associated with the selective transmission of the blue-green and red-violet light rays).

The colouring is caused by the admixture of the Cr3+ (it contains about 0.3% of the Cr2O3 by the mass). The crystals are tabular, there are characteristic the hexagonal pseudohexagonal trillings with the feather hatching on the edges. The hardness is 8.5. The density is 3700 ± 200 kilograms per cubic metre. It may be found in the emerald-bearing biotite-phlogopite micas among the metamorphosed ultramafic rocks. The main deposits are in the Sri Lanka (placer deposits), India, South Africa, in the USSR at the Middle Urals mountain range.

Alexandrite is the gemstone of the II order. It is imitated by the synthetic corundum or spinel with the admixture of the vanadium.