Zircon Stone
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| Blue Zircon from Cambodia |
Zircon is an important jewelry stone, but is not well known by the general public. In fact many people who are aware of zircon confuse it with the diamond simulant cubic zironia. They are of course completely different. Cubic zirconia is a lab-created material while zircon is a natural mineral with a very different chemical composition.
Zircon belongs to the large group of minerals known as neosilicates that contain both silicon and oxygen in their composition. The group includes the various garnets, peridot, topaz, andalusite, kyanite, tanzanite, the various beryls, tourmaline and quartz. Zircon is a zirconium silicate, and is the main source of the element zirconium, a lustrous white-gray metal resembling titanium.
Zircon is important in the gemstone world because of its very high refractive index (1.810-2.024), approaching that of diamond (2.417-2.419). Zircon combines exceptional brilliance with impressive dispersion or fire, the tendency to split white light into the spectral colors. Indeed, in the days before diamond simulants like cubic zironia and moissanite, inexpensive white zircon was popular as a substitute for diamond and was often sold under the misleading name "Matura Diamond."
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| Orange Zircon |
Green Zircon |
White Zircon |
Yellow Zircon |
However, zircon occurs in a range of interesting colors, of which white is probably the least important. The most popular color of zircon in today's market is a light electric blue with pleochroism making it look greenish in one direction. This blue zircon is produced by heat treatment. But only some zircon has the right physical structure to turn blue when heated. This is why most blue zircon comes from Cambodia or Burma.
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| Orange Rose Zircon from Tanzania |
Some colors of natural zircon are not treated in any way. They include rare rose and rose-orange from Tanzania and orange and orange-brown from Cambodia. Green zircon is very rare; this unusual color is caused by minute radioactive elements of uranium and thorium. Yellow or gold zircon is usually heat-treated to improve the color, though untreated specimens can sometimes be found.
Although reasonably hard, (rating 6.5-7.5 on the Mohs scale), zircon is somewhat brittle and therefore sensitive to knocks and pressure. Zircon has the tendency to wear along facet edges. Its use in rings should therefore be limited to protective settings or occasional wear jewelry.
Zircon can be found in a number of locations in Asia, especially Cambodia, Vietnam, Thailand, Burma and Sri Lanka. African sources are becoming more important, with zircon found in Tanzania, Madagascar, Mozambique and Nigeria.
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