Sapphire (Greek: sappheiros, ‘blue stone’, is a typically blue gemstone variety of the mineral corundum, an aluminium oxide. Trace amounts of elements such as iron, titanium, chromium, copper, or magnesium can give corundum respectively blue, yellow, purple, orange, or green colour. Because of the remarkable hardness of sapphires – 9 on the Mohs scale (the third hardest mineral, after diamond at 10 and moissanite at 9.5), sapphires are used in some non-ornamental applications, including infrared optical components, such as in scientific instruments. The cost of natural sapphires varies depending on their colour, clarity, size, cut, and overall quality – as well as their geographic origin. Significant sapphire deposits are found in Eastern Australia, Thailand, Sri Lanka, Shandong (China), Madagascar, East Africa, and in North America in a few locations, mostly in Montana. Some famous sapphires are listed here:
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The Star of India (mined in Sri Lanka), weighing 563.4 carats, is thought to be the second-largest star sapphire (the largest blue), and is currently on display at the American Museum of Natural History in New York City.
The 182-carat Star of Bombay, mined in Sri Lanka, located in the National Museum of Natural History, in Washington, D.C., is another example of a large blue star sapphire.
Gemological Institute of America Website: