Zircon

Zircon illustration Leon Mege

Natural zircon is a greatly underrated gemstone, in part because it was a very popular diamond simulant in the early 1900s. Cubic zirconia, colorless moissanite, and lab-grown diamonds are better substitutes, rendering zircon useless as a fake diamond. However, the name zircon still carries the stigma associated with its checkered past.

Zircons are double-refractive. They show a degree of birefringence, which is doubling-up of facets which makes it easy to distinguish them from single-refractive
gems like diamonds. Although birefringence may detract from brilliance, it is an unusual optical feature that should be appreciated for its uniqueness.

Zircon is relatively hard (7.5 on Mohs scale) and has exceptional fire due to its strong dispersion. Colorless zircon is known for its brilliance and fire. Zircon’s high specific gravity always stands out among other similar looking gems. 

Natural zircon is known for its distinctive beauty and occurrence in a broad range of colors. It can be blue, green, colorless, grey, brown, red, orange, or yellow.

Zircon naturally comes in several colors; blue is the most popular variety due to its vivid vibrance. The blue zircon is not only outstanding and comparable to the natural blue in diamonds and aquamarines, but it is also much more affordable. The darling of the Victorian era, the blue zircon remains the most popular color even now. The most desirable electric-blue zircons are heat-treated brown crystals found mainly in Cambodia.

Yellow is the most iconic color of zircons. Until diamond deposits in Africa yielded plenty of colorless diamonds, the pale yellow zircons were used to fool unsuspecting buyers into thinking they were getting a Brazilian diamond. Although the most popular color is blue, the canary yellow and honey colors are gorgeous, and they are an important yellow gemstone on the jewelry palette.

An unusual property called thermochromism occurs when some yellow zircons from Kaduna, Nigeria, and Singida, Tanzania, cycle from brown to vivid orange when gently heated. Heating it with a cigarette lighter for about 20 seconds will do the trick. Once zircon cools down, the process can be repeated.

Red zircons occasionally have a curious physical property called tenebrescence – quickly turning dark-brown or even black when exposed to sunlight after being kept in the dark. Once zircon gets too hot, it will turn colorless, and all the tenebrescent and thermochroic properties will be lost. 

The rarest zircon color variety is green, sometimes called beccarite. Green zircons are usually olive-green, similar to peridots.

Taaffeite, or pink zircon, was first discovered in 1945 by Dublin gemologist Richard Taaffe who found at the local jeweler what he initially thought was a pale mauve spinel. The double-refractive gem was identified as a new zircon species upon further testing. Not until four years later, another taaffeite was found in a parcel of Sri Lanka gems. 

 

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