Pyrite

The mineral pyrite or iron pyrite is iron disulfide, FeS₂, its isometric crystals usually appearing as cubes or pyritohedrons. It has a slightly uneven and conchoidal fracture, a hardness of 6-6.5, and a specific gravity of 4.95-5.10. Its metallic lustre and pale to normal brass-yellow color have earned pyrite the name "fool's gold," but ironically enough small quantities of actual gold can sometimes be found in pyrite (to the point where some auriferous pyrite is a very valuable ore), as well as arsenic, nickel, cobalt and copper.

A mass of interwoven pyrite crystals,
11 cm (4.0 in) long

Pyrite is the commonest of the sulfide minerals, and is found world-wide. It is found associated with other sulfides, or with oxides, in quartz veins, in sedimentary rock and metamorphic rock, in coal beds, and as the replacement mineral in fossils. Pyrites, interestingly, can show negative resistance, acting as radio detectors and have been used in oscillator circuits.

Pyrite is used in the production of sulphur dioxide for the paper industry and in the manufacture of sulphuric acid, though not as much as it used to be. The name pyrite is from the Greek word meaning fire. because of the sparks that result when pyrite is struck with steel.