Periot (pronunciation: /ˈpɛrɪˌdɒt/, /ˈpɛrɪˌdoʊ/ (British English), /ˈpɛərɪˌdɑt/, /ˈpɛərɪˌdɑʊ/ (US English)) is the gem quality variety of forsteritic olivine. The chemical composition of peridot is (Mg, Fe)2SiO4, with Mg in greater quantities than Fe. The name of the gemstone is believed to come from either the Arabic word faridat, meaning "gem", or from a Greek word meaning "gold stone". Peridot is one of the few gemstones that comes in only one color. The depth of green depends on how much iron is contained in the crystal structure, and varies from yellow-green to olive to brownish green. Olivine is a very abundant mineral, but gem quality peridot is rather rare. Peridot crystals have been collected from some Pallasite meteorites. Peridot olivine is the birthstone for August.