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A precious stone that is a red variety of a transparent corundum. The colour ranges from pink to deep red; the pigeon’s-blood ruby is deep red tinged with purple. Flawless specimens showing the most desirable colours are rare; the varieties of shades are due to the presence of a small quantity of oxide of chromium. Some rubies show asterism. Rubies may be cut as brilliants, but more often are mixed cut; sometimes they are cut and strung as beads.
They are occasionally termed ‘true ruby’, ‘red corundum’, or ‘Oriental ruby’. The principal sources are the Mogok district of Upper Burma for deep-red rubies, Sri Lanka (formerly Ceylon) for light red, and Thailan (formerly Siam) for dark brownish-red. The best rubies are more costly than diamonds of the same size, and are exceeded in value only by the emerald. Rubies contain some tiny irregular inclusions; synthetic rubies have bubbles that are perfectly rounded instead of being natural crystal shapes, and can be further identified by having striae in straight rather than curved lines. Among the famous true rubies are Anne of Brittany’s Ruby; De Long Star Ruby; Edwardes Ruby; Peace Ruby; Rosser Reeves Star Ruby. Some well-known so-called rubies (known as a Balas ruby or ruby spinel) are in fact red spinel.