Zircon

Zircon Group. The zirconium analogue of Thorite and Hafnon. Zircon-Hafnon Series. The low-pressure dimorph of Reidite. Zircon, zirconium orthosilicate, is found in most igneous rocks and some metamorphic rocks as small crystals or grains, mostly widely distributed and rarely more than 1% of the total mass of the rock. It is also found as alluvial grains in some sedimentary rocks due to its high hardness. Zircon has a high refraction index and, when the crystals are large enough, is often used as a gemstone. In geology, zircon is used for radiometric dating of zircon-bearing rocks (using isotopes of U which is often present as an impurity element, as is Th, radiogenic Pb, Hf, Y, P, and others). The uranium concentration of zircon is generally very high, between 300 and 600 ppm and a melting temperature of 2550 °C, making zircon a good mineral for age dating. Compare 'UM1984-36-SiO:CaNaZr'.