sapphire, precious stone. A transparent blue corundum , it is classified among the most valuable of gems. Sapphires are found chiefly in Madagascar, Sri Lanka, and Myanmar and also in Thailand, Tanzania, Australia, Cambodia, and in the United States (in Montana). The sapphires from Kashmir, which is no longer a significant source of the gems, are of a beautiful cornflower blue and are highly valued. The Sri Lankan and Madagascan varieties are paler; those from Montana have a metallic luster; those from Myanmar are a dark royal blue; 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. Natural sapphires may be heat-treated to enhance their color. 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.
See more Encyclopedia articles on: Mineralogy and Crystallography