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.
More on ruby from Fact Monster:
See more Encyclopedia articles on: Mineralogy and Crystallography