Zircon

Zircon is a mineral with the chemical formula ZrSiO4. It is a nesosilicate that crystallizes in the tetragonal system and occurs in a wide range of igneous and metamorphic rocks. The name zircon is derived from a Persian word meaning gold-colored, reflecting some of the mineral’s early color varieties.

In terms of properties, zircon is relatively hard and dense, with a hardness of about 7.5 on the Mohs scale and a high specific gravity of roughly 4.6 to 4.7. It exhibits a high refractive index and strong dispersion, which can give zircon notable brilliance when cut as a gemstone. Zircon commonly shows colors from colorless to yellow, brown, red, green, or blue, depending on trace impurities and radiation damage. Many zircon crystals contain traces of uranium and thorium, which over time can cause metamictization and influence the mineral’s properties.

Zircon is widespread in continental crust and is especially common as an accessory mineral in granitic and pegmatitic rocks. It also forms in metamorphic rocks and can be a major component of placer or detrital sands. Because zircon is chemically resistant and often accumulates in ancient rocks, it is widely used in geochronology; uranous and thorium decays provide U-Pb dating data that can date rocks billions of years old.

As a gemstone, zircon is valued for its natural brilliance and fire, with colorless stones sometimes used as diamond substitutes. It is important to distinguish natural zircon from synthetic cubic zirconia, which is a different material used as a diamond simulant. Zircon crystals are among the oldest known minerals, with some samples dating back about 4.4 billion years.