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 2.5% chromic oxide have the prized pigeon-blood red colour.