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December - Birthstones

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Blue Zircon - Arabic for "vermilion" - December

Although the name zircon comes from the Arabic "zargoon' meaning vermilion or golden colored, zircons also occur in a wide range of subtle greens and browns and are occasionally colorless. Such stones have been used for many centuries in Indian and Sinhalese jewelry. In western jewelry zircons are most familiar as lustrous and fiery vivid blue, golden or colorless stones which are usually cut as round brilliants. These colors are produced artificially by heating brown zircon from Thailand, Kampuchea and Vietnam. Heating in an oxygen-free atmosphere produces blue zircon, which may then be heating in air to give the golden color. Both processes produce some colorless material. Heat-induced colors sometimes fade on exposure to light but may be restored by careful reheating. Zircon resembles diamond in its fine lustre and fire, so that colorless stones have been both mistakenly identified as diamonds and purposely used as diamond stimulants. Zircon is easily distinguished by signs of wear and double refraction. Although zircon is moderately hard it can be very brittle, and the facet edges of cut stones are easily chipped in wear. It is also strongly doubly refractive, the facet edges appearing doubled when viewed through the stone. Zircon contains traces of uranium or thorium which produce a distinctive absorption spectrum. Radiation from these elements may gradually disrupt and transform the tetragonal crystalline structure to a "metamict" state. Such zircons are usually green and cloudy, show only slight double refraction, and have lower refractive indices, density and hardness