Pyrite

Pyrite is the most common form of the sulfide minerals. It is usually found associated with other sulfides and oxides in quartz veins, sedimentary rock and metamorphic rock, as well as in coal beds, and also as the replacement mineral in fossils.

Pyrite exposed to the environment during mining and also excavation reacts with oxygen and water to form sulfuric acid, resulting in acid mine drainage. This results from the action of Trio bacillus bacteria, which generate their energy by using oxygen to oxidize ferrous iron (Fe2+) that ferric iron (Fe3+). The ferric iron in turn reacts with pyrite to produce ferrous iron and also sulfuric acid. The ferrous iron is then available for oxidation by the bacteria; this cycle could continue until the pyrite is exhausted

Colour and Value

The mineral pyrite, and iron pyrite, is iron disulfide, FeS2. It has isometric crystals, which usually appear as cubes. The cube faces could be striated (parallel lines on crystal surface or cleavage face) as a result of alternation of the cube and pyritohedron faces. Pyrite also frequently occurs as the octahedral crystals and as pyritohedron (a dodecahedron with pentagonal faces). It has a slightly uneven and concordat fracture, a hardness of 6–6.5, and a specific gravity of 4.95–6.10. It is brittle, meaning it breaks and powders easily. Its metallic luster or pale-to-normal brass-yellow hue have earned it the nickname fool's gold, but ironically, small quantities of the actual gold is sometimes found in pyrite. In fact, such auriferous pyrite is a very valuable ore of gold.

The name pyrite is from the Greek word "Pyr" meaning "fire". This may be likely due to the sparks that result when pyrite is struck against steel. This capacity made it very popular for use in early firearms such as the Wheelock.

In her historical fiction book The Valley of Horses, Jean Auel's heroine Ayla is described as discovering a new method of creating fire by striking a pyrite-like material against flint.

Uses

• Pyrite is used for the production of sulfur dioxide, e.g. for a paper industry, and in the manufacture of sulfuric acid, though such applications are declining in importance.

• Pyrites could show negative resistance and have experimentally been used in oscillator circuits as radio detectors.