Zircon is also known as ‘zircon quartz’ or ‘hyacinth stone’, and the chemical formula is Zr(SiO4). It usually contains hafnium, niobium, tantalum, thorium, and uranium. Its crystals belong to the tetragonal system. The crystals have a tetragonal columnar form or tetragonal twins, and the aggregates are granular. It has an adamantine lustre, a specific gravity of 4.7, and a Mohs hardness of 7–8. It mainly forms in igneous rocks, especially alkaline rocks. Zircon is heat-resistant (melting point of 2,750 °C) and corrosion-resistant. It is generally used in the foundry industry as well as for manufacturing acid-resistant and fire-resistant glassware. It is also the raw material for the extraction of zirconium and hafnium. As it has a high refractive and dispersion index, colourless and transparent zircon has become a substitute for diamond. Gem-grade zircons are mainly clastic minerals found in gravel layers. The major production countries include Sri Lanka, Thailand, Laos and Cambodia.