Zircon

Zircon (ZrSiO₄) is a minor gem, but a valuable source of zirconium metal and a major mineral for today's geologists. Zircon always occurs in crystals like this 8-millimeter twinned specimen from Mexico, although the middle may be stretched into long prisms. Most often brown, zircon also can be blue, green, red, or colorless. Gem zircons are usually turned blue by heating brown or clear stones.

Zircon has a very high melting point, is fairly hard (Mohs hardness 6.5–7.5), and is resistant to weathering. As a result, zircon grains can remain unchanged after being eroded from their mother granites, incorporated into sedimentary rocks, and even metamorphosed. That makes zircons valuable as mineral fossils. At the same time, zircons contain traces of uranium suitable for age dating by the uranium-lead method. They are the gold standard for dating ancient granites, which can be hard to date with other methods.

Learn more about zircon and other zirconium minerals.

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