n (mineralogy) The common mineralirondisulfide (FeS2), of a pale brass-yellow color and brilliant metallic luster, crystallizing in the isometric system.
n (usually as a plural: 'pyrites') Any metallic-looking sulphide, such as the above, which is the most common
n (context|solid state|_|chemistry) (usually as a plural: 'pyrites') Any metal dichalcogenide that is isostructural to the common mineral