Ruby crystal before faceting.
Ruby is a deep red gemstone, a variety of corundum colored by a minute proportion of chromium ions. It is found significantly in upper Burma, Thailand, and Sri Lanka, and is far more precious than diamond. The name has been used for other red stones, chiefly varieties of garnet and spinel. Rubies have been synthesized by the Verneuil flame-fusion process (1902). They are used to make ruby lasers