From Longman Dictionary of Contemporary Englishpyritespy‧ri‧tes /paɪˈraɪtiːz $ pə-/ noun [uncountable] 
HEGa mix of sulphur with a type of metal, usually iron, or iron and copper → fool’s gold iron pyrites
HEGa mix of sulphur with a type of metal, usually iron, or iron and copper → fool’s gold iron pyritesExamples from the Corpus
pyrites• When the wetlands are drained the iron pyrites in the soil are exposed to air and form sulphur acid.• The scientists warn that the deposits of pyrites are too large to neutralize by liming.Origin pyrites (1500-1600) Latin “flint”, from Greek, “of or in fire”, from pyr; → PYRE 