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.
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.
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.