Chrysoberyl, and the Eye That Opens

Chrysoberyl is beryllium aluminium oxide, a distinct species from beryl despite the similar name, and at hardness 8.5 it is one of the hardest gems after diamond, corundum and moissanite. It is best known through two remarkable varieties. Alexandrite contains chromium and appears green in daylight and red under incandescent light, a colour-change first noted in Russian deposits in the nineteenth century. Cat's-eye chrysoberyl shows a sharp band of light, chatoyancy, produced by parallel needle inclusions; the trade name cymophane belongs to it, and among gems the term cat's-eye without qualification means chrysoberyl specifically. In Indian astrological practice cat's-eye chrysoberyl is the stone assigned to Ketu, one of the nine navaratna gems, which is a documented tradition; the general metaphysical attributions attached to plain chrysoberyl in modern sources are recent.

George Frederick Kunz, the American gemologist whose The Curious Lore of Precious Stones (1913) remains the standard survey of stone-lore, records that in Ceylon (modern Sri Lanka), the historic source of the finest cat's-eye chrysoberyl, the stone was carried as a defence against the evil eye and against sudden ill fortune, and was especially prized by gamblers hoping to hold their luck. Kunz also notes the old naming confusion that dogs the species: nineteenth-century mineralogists and jewellers sometimes called chrysoberyl chrysolite, a name properly belonging to peridot, so older references to a chrysolite gem cannot be read with confidence as either stone without other evidence.