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Zircons can be mildly radioactive, containing trace amounts of the chemical elements uranium (U), thorium (Th), and the transition metal hafnium (Hf) is typically present in zircon. Using radiometric dating, zircons found in Western Australia's Yilgarn Craton and Narryer Gneiss Terrane are some of the oldest minerals found on earth, at 4.4 billion years. Zircon Color & RefractionZircon occurs in a wide varieties of colors which include: brown, orange-red or yellow (jacinth), red or violet-red (hyacinth), as well as green, blue, and black. There is also a colorless zircon called jargoon, which can be mistaken for diamond. Sri Lanka has a clear variety of zircon that is referred to as "Matara diamond," and is a popular, yet inexpensive diamond substitute. What makes zircon particularly appealing as a faceted gemstone is its high refractive index (1.90 average, compared to diamond's refractive index of 2.4), and its diamond-like adamantine luster, yet this is where the similarity with diamonds diverges. Zircon has a hardness of only 7.5 on the Moh's scale, and the toughness, or "tenacity" of zircon is only rated as fair to good. It is for this reason that care must be taken to avoid chipping or abrading the facet edges.  Unlike diamond, zircon is both doubly refractive and anisotropic, with varying refractive indices along its a or b crystallographic axes. Zircon is also one of the heaviest gemstones, resulting in smaller sizes (measured in milimeters) for a given carat weight. Zircon Crystallography, Chemistry, Physical Properties
Zircon Optical Properties
Transparent zircon can be found in shades of brilliant green, brownish-green and yellow-green. These stones typically have unique inclusions known as "spangles," as well as streaks and/or angular color zoning. Yellow zircon can be mistaken for yellow sapphire, and can be found in the canary yellow, greenish yellow, and golden-yellow. Perhaps the most popular gemstone color for zircon is blue.
Zircon Color EnhancementsZircon can be heat treated to alter its color, and varying temperatures can produce colorless, blue, or yellow gems from less desirable specimens. Heat treatment of reddish-brown stones found in Cambodia, Thailand, and Vietnam produce most of the blue zircon gemstones on the market, but many of the red, red-orange, or violet-red zircon on the market has not undergone any kind of heat treatment. The resulting color change of heat-treated zircon is permanent. To date, there are no examples of a synthetic zircon. Zircon MiningThe principal sources for zircon are found in Cambodia, Thailand, and Sri Lanka. Colorless varieties of zircon from Matara, Sri Lanka has become synonymous with fake diamonds, and have come to be known as "matara diamonds." There is also a chatoyant variety of zircon found in Sri Lanka. Zircon is mined for its zirconium, which is used as a compound in abrasives, and it is also the source for zirconium oxide which is one of the most refractory (high-temperature, high-strength) materials known, used in high-temperature crucibles and nuclear reactors [3]. 
Bibliography and Reference on Zircon 1. Wuerzburg Uniaxial Minerals - Zircon 2. Edna B. Anthony The Zircon Group - A Nesosilicate 3. Stephen A. Nelson Introduction to Uniaxial Minerals 5. Judith Crowe, The Jeweler's Directory of Gemstones 6. Walter Schumann, Gemstones of the World 7. Renee Newman, Gemstone Buying Guide 8. Africa Gems, Cut Zircon | Copyright © 2012 AllAboutGemstones.com. All rights reserved. | | | ||||||||||||||||||||||||||||||||||||||||||||||||
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: Zircon
