ruby, precious stone, the transparent red variety of corundum, found chiefly in Myanmar, Thailand, and Sri Lanka and classified among the most valuable of gems. The Myanmarese stones are blood red, the most valued tint being the "pigeon's blood." The Thai stones are darker and the Sri Lankan stones lighter than the Myanmarese specimens. Star rubies, i.e., those that show an internal star-shaped formation when cut in cabochon (with a rounded top), are rare. Synthetic rubies are manufactured by the fusion of pure aluminum oxide. Chromium oxide is added to provide the appropriate color.

Gemstone composed of transparent red corundum. Its colour varies from deep to pale red, in some cases with a tinge of purple, depending on chromium and iron content; the most valued is a pigeon-blood red. When it is cut and polished, ruby is a brilliant (light-deflecting) stone, but it lacks fire (flashes of colour). Ruby is a mineral of very limited distribution. Its best-known source is in Myanmar, and rubies have also been found in Thailand, Sri Lanka, and elsewhere. Rubies have been produced synthetically with much success; those containing 2.5percnt chromic oxide have the prized pigeon-blood red colour.

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