A type of quartz. Its name originates from the Sanskrit word "upala" meaning precious stone. They are luminous and iridescent with inclusions of many colours. Opals show a shifting of spectral colours. They are found in Mexico, Brazil, the USA, Japan, Honduras, Kenya, Czechoslovakia, Peru, Canada. By far Australia is the main source of opals, almost ninety-five per cent of all fine opals come from the dry and remote outback deserts.

Source: Encyclopedia of gemstones and minerals.