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Smithsonian National Museum of Natural History

Zircons

Heat treatment of natural reddish brown stones yielded these brilliant gems.
Photo by Penland. Click to zoom.
SpecimenCatalog NumberLocalityWeight
ZirconNMNH G3568-00Shantaboon, Thailand105.9 ct
ZirconNMNH G3554-00Sri Lanka48.3 ct
ZirconNMNH G2237-00Sri Lanka97.6 ct
ZirconNMNH G2222-00Thailand103.2 ct

Gift of Roebling Fund.

Most gem zircons are found as waterworn pebbles in gravel deposits in Thailand, Cambodia, Vietnam, and Sri Lanka. Other localities include Burma, Madagascar, Brazil and Tanzania. Zircon is typically brown, reddish-brown, green or yellow. Since the 1920s virtually all zircon gemstones used in jewelry have been heat-treated to enhance their colors, producing blue, golden, and some colorless stones. Colorless zircon outperforms any other mineral imitating diamond as its dispersion and brilliance is almost as good as that of diamond. However, its inferior hardness and brittleness reveal zircon as an imposter. Like diamonds, zircons are typically cut as round brilliants to best show their dispersion or fire. The most popular zircons are the blue, colorless, and golden gems produced by heating.

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