Pyrite

Nicknamed "Fool's Gold" for people frequently mistaking it for gold, pyrite is the most common sulfide mineral and is found in a wide variety of geological formations. It is often mined for the gold or copper associated with it and is a source of sulfur for sulfuric acid. The name is from a Greek word meaning "fire" for the sparks that flew from it when hit with another mineral or metal.

Mineral Photos courtesy of R.Weller/Cochise College