Zircon is a naturally occurring gemstone . . . and should not be confused with the recently
created Cubic Zirconia.
For many centuries, the brilliance of zircon has captured the hearts of those who set
their eyes on this magnificent gemstone. Zircon’s popularity began to grow in the sixth
century, when Italian artisans featured the stone in jewelry designs. During the Middle
Ages, zircon was believed to contain remedial power, protecting the wearer from diseases
and banishing insomnia. The name "zircon" is believed to have derived from the Arabic words,
"zar", meaning gold, and "gun", meaning color.
Zircon is gemmologically interesting because it occurs in many varying forms. It is found
in Sri Lanka, Mogok area of Burma, Espaly-Saint-Marcel in France, Arendal in Norway, Uralla,
Sapphire Inverell in New England, New South Wales in Australia, and elsewhere.
Coloration
Zircon occurs naturally in a large range of colors including: yellow, red, orange, brown,
green, and blue. Heat treatment is often used to produce stones which are colorless,
golden brown, or sky blue. Many of the available colours are very attractive, and Zircons
also have a high dispersion, and therefore show good "fire". Probably the best known color
is the very startling blue. Zircon is slightly brittle, and therefore should not be
ill-treated, but otherwise it is quite durable and suitable for use in jewelry.
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The great variability of Zircon is caused by the natural radioactive decay of small amounts
of uranium or thorium causing the crystal structure to break down into amorphous silica and
zirconia. Heat treatment appears to reverse much of the deterioration in the crystal
structure, so that "low" types can be converted successfully to "high" types. There are also
intermediate types.
Sources
Thailand and Cambodia are the world’s major suppliers of zircon with large deposits near
the border of the two countries. Vietnam, Burma, Sri Lanka and Africa also provide a large
supply of these marvelous gemstones to the world market.
Technical Characteristics
Usually there is partial replacement of the zirconium by iron, hafnium, thorium and uranium.
There are three natural types of Zircons: low, medium and high. The variance is due mainly
to the differences in the specific gravity and refractive index.
Having the highest refractive index among any natural gemstones, with the exception of
diamonds, the brilliance of high Zircon is second to none. As temperature rises, the
refractive index of zircon also increases, making the gems even more spectacular. Despite
its brilliance, Zircon is quite brittle and can easily be chipped or scratched. When setting
Zircon jewelry care need be taken to make a protective mount. Therefore zircon earrings and
Zircon necklaces are the more obvious choices but Zircon rings need not be discounted
simply treated with respect.
A very unique characteristic of zircon is birefringence, meaning that light splits into
two rays as it passes through the stone. As a result, the back facets appear as double images.
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Chemical Composition:
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Zirconium Silicate ZrSiO4
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Hardness:
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6.5 - 7.5 (Variable)
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Specific Gravity:
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4.60 to 4.70, usually 4.69
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Refractive Index (R.I.):
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1.92 to 1.98
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Bi-refringence:
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0.059
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Optic Sign:
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Positive
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Optical Character:
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Uniaxial
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