pyrite

1. (mineralogy) The common mineral iron disulfide (FeS₂), of a pale brass-yellow color and brilliant metallic luster, crystallizing in the isometric system.Examples: "The pyrite output in 1961 was 1.2 million tons, derived mainly from the Hsiang Shan mine in Anhwei and the Ying-te mine in Kwangtung."; "China's 13 large foreign fertilizer plants ordered a few years ago are all scheduled to be in operation in a year or two.[…]China's biggest pyrite mine (openpit), being built in Yunfu, Kwangtung Province, was near completion."

2. (usually as a plural: pyrites) Any metallic-looking sulphide, such as the above, which is the most common.usually

3. (solid state chemistry) (usually as a plural: pyrites) Any metal dichalcogenide that is isostructural to the common mineral.Examples: "Copper diselenide can occur both as a marcasite and a pyrite."