Pyrite

(′pī′rīt)

(mineralogy) FeS₂ A hard, brittle, brass-yellow mineral with metallic luster, crystallizing in the isometric system; hardness is 6-6.5 on Mohs scale, and specific gravity is 5.02. Also known as common pyrite; fool's gold; iron pyrites; mundic.

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A mineral having composition FeS₂. Pyrite has a Mohs hardness of 6–6.5 and a density of 5.02. The luster is metallic, the color brass yellow, and the streak greenish black or brownish black.

Pyrite, or iron pyrites, is the most common “fool's gold,” but it is hard and brittle whereas gold is soft and sectile. Its hardness also distinguishes it from softer chalcopyrite. Marcasite was once thought to be polymorphous with pyrite, but precise analyses show that marcasite contains excess iron, whereas pyrite is stoichiometric FeS₂. See also Marcasite.

Pyrite is the most common and most widespread sulfide mineral. It forms under almost all known conditions of mineral deposition. Under oxidizing conditions, pyrite readily alters to iron sulfates and eventually to limonite, forming gossan, the surface expression of pyrite-rich mineral deposits. See also Limonite.

Because of its high sulfur content (53.4%), pyrite has become a source of sulfur for the production of sulfuric acid. In some places, it is mined for sulfur alone. See also Sulfur.

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Iron pyrite (FeS₂) is a mineral popularly known as "fool's gold." Because of its metallic luster and pale brass yellow color, it is often mistaken for gold. Real gold is much heavier, softer, not brittle, and not grooved.

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