The mineral pyrite, or iron pyrite, is iron sulfide, FeS2. It has isometric crystals that usually appear as cubes. The cube faces may be striated (parallel lines on crystal surface or cleavage face) as a result of alternation of the cube and pyritohedron faces. Iron Pyrite also frequently occurs as octahedral crystals and as pyritohedra (a dodecahedron with pentagonal faces). It has a slightly uneven and conchoidal fracture, a hardness of 6–6.5, and a specific gravity of 4.95–5.10. It is brittle.  A major identifier, useful in the field, is the streak, as the powdered mineral smells of sulfur. Its metallic luster and pale-to-normal brass-yellow hue have earned it the nickname fool's gold, but ironically, small quantities of actual gold are sometimes found in pyrite. In fact, such auriferous pyrite is a valuable ore of gold. The name pyrite is from the Greek word "Pyr" meaning "fire". This is likely due to the sparks that result when pyrite is struck against steel. This capacity made it popular for use in early firearms such as the wheellock.

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