| Sapphire is an aluminum oxide. Its color varies from very light to dark blue and varieties of colorless (white sapphire), yellow, violet, pink, green and the pinkish-orange (padparadscha sapphire).Sapphires are generally treated with x-ray and heat to intensify their color. Natural sapphires undergo heat and diffusion treatments almost always. Treatment of blue stones is permanent.Ceylon SapphiresThe Ceylon Blue Sapphire is known for its beauty – possessing the glorious cornflower blue shade – as well as for being one of the few sapphires in the world that can be sold as a completely natural stone without heat treatment. The blues aside, Ceylon sapphires also come in beautiful hues including pink, yellow, orange, green, purple, lavender and of course, the inimitable padparadscha sapphire (Pink-Orange). All these highly marketable qualities of Ceylon sapphire has created brand recognition world wide - a brand not created by the producers of the stone, but by the sellers and consumers.Sapphires that show a star-like light effect are called star sapphires; the most famous star sapphire from Sri Lanka is displayed in the Museum of Natural History in New York. Star sapphires or star rubies display a star-like marking and this effect, commonly known as asterism, occurs when light falls on the cut stone, cut in the cabochon form, and three rays appear giving a six-point star.Lastly, there is milky corundum, a white opaque form of corundum also called geuda, which for many years was regarded as useless and discarded, often ending up lining fish tanks in some gemstone merchant's house. This happened until dealers in Thailand learned to heat-treat geudas to change the color of the stone from an unattractive cloudy grey-white to a bright, sparkling blue. They completed the work nature began and ended up with a blue sapphire - of much greater value than a useless pebble. The color of heat-treated blue sapphires are stable and the chemical composition of the stone is that of a sapphire, although prices are lower than for a similar quality stone with natural color.
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