Blue and colorless zircons are almost always heat treated. For this reason, high heat and prolonged exposure to ultraviolet light (including tanning beds) should be avoided to prevent changing the stone's color. Harsh daily wear should also be avoided, as zircon can be brittle and become abraded from sharp knocks. It has very good hardness (8 on the Mohs scale of 1-10) and resists scratching. Warm soapy water or an amonia-based cleaner are ideal for cleaning zircon. Like most colored stones, zircon's value is primarily determined by its intensity and saturation of color, all other factors being equal. Beyond that, size and clarity play an important role. Most gem zircons are eye-clean. Blue and colorless zircons are considered type I gems, meaning they are almost always eye clean. Other colors of zircon are type II; they can show eye-visible inclusions, but this should not take away from the stone's beauty. Fine cutting can dramatically bring out zircon's natural briliance and increase its value. Because blue zircons are in higher demand, they are usually more expensive than other zircons, but reds, pinks and purples are some of the rarer colors. The warm chocolate, honey and golden shades are popular with today's fashions, and provide an affordable natural alternative to fancy colored diamonds.
Radiant zircon is perhaps the most misunderstood of all gemstones. Unfortunately due to the similarity of zircon's name to the diamond simulant cubic zirconia, many people don't realize that zircon is a beautiful, naturally occurring stone with its own merits. It has been a less-expensive stand-in for many gems throughout history, notably diamond. Zircon has tremendous fire and a dispersion rate nearly as high as diamond and much higher than other gems.
The fire in zircon, called dispersion, is caused by light entering the gemstone and separating into a prism of rainbow colors. Possessing dispersion and brilliance approaching that of diamond, the brilliance of zircon is highly regarded. Dispersion is best observed in pale to colorless stones, as the deeper colors can mask this property. The zircon cut, a variation of the round brilliant cut that adds eight extra facets to the pavilion, was designed to take advantage of these properties.
Zircon also has an adamantine (diamond-like) luster, lending further credence to its suitability as a diamond substitute. Another interesting characteristic of zircon is that its birefringence (double refraction, meaning that light splits into two rays as it passes through the gem) is great enough to produce visible doubling of the back facets in larger stones. This property makes it easy to separate from diamond, but the affect can be minimized when the cut is oriented properly.
Cambodia is the world’s premier source for gorgeous blue zircon. Remote, pristine and stunningly beautiful, Ratanakiri province is the major center for Cambodian zircon, yielding most of the world’s finest blue zircon. Ratanakiri literally means “gemstone mountain.” Zircons here are a light beige to dark honey color when they are mined, but change to blue upon heating. Further heating can make them colorless. Cambodian zircons are traditionally cut and processed in neighboring Thailand, just a short trip across the border.
Burma is known for producing green and yellow zircons, but small amounts of all colors have been found there. Vietnam also produces some material similar to the Cambodian zircon, but in smaller quantity. Sri Lanka was once a major producer of zircon and still produces some, but has been eclipsed by the Cambodian production in recent years. East Africa produces mainly intensely colored zircons in the brown to red shades. These stones will not heat to blue like the Cambodian material, but they will change to rose and imperial hues that have a beautiful sherry to rose` color, often resembling fine imperial topaz.
Unusual among gems, zircon has a small amount of uranium or thorium. This gives zircon a diagnostic absorption spectrum, but any radioactivity remains well within safe levels and can only be detected by the most sensitive of instruments. Zircon also occurs as minute inclusions within certain sapphires and rubies and offers clues as to the origins of the gems that contain them.