sapphire, precious stone. A transparent blue corundum , it is classified among the most valuable of gems. Sapphires are found chiefly in Thailand, India, Sri Lanka, and Myanmar and also in Australia and in the United States (in Montana). The sapphires from Kashmir are of a beautiful cornflower blue and are highly valued. The Sri Lankan varieties are paler those from Montana have a metallic luster and the Australian sapphires are of a dark blue shade approaching black. The terms yellow sapphire, purple sapphire, and green sapphire are used alternatively with Oriental topaz, Oriental amethyst, and Oriental emerald for other varieties of corundum. Like rubies of similar structure, some sapphires display a six-pointed star when cut to a cabochon (round-topped) shape and exposed to direct sunlight. Such star sapphires are usually obtained from Sri Lanka. Synthetic sapphires are made by the fusion of aluminum oxide, with titanium oxide added as a coloring agent.

The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.

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