Zircon occurs in many colors, including reddish brown, yellow, green, blue, gray and colorless. In addition, the oxygen isotopic compositions of some of these zircons have been interpreted to indicate that more than 4. Occurrence[ edit ] World production trend of zirconium mineral concentrates Zircon is a common accessory to trace mineral constituent of most granite and felsic igneous rocks. Their average size in granite rocks is about 0. Because of their uranium and thorium content, some zircons undergo metamictization.