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.