.Pyrite Mineral Facts:

Chemical Formula: FeS₂  The Mineral is 46.6% Iron by weight.
Iron disulphide, FeS₂ = Sulphur 53.4, iron 46.6%. Sometimes contains small amounts of nickel, cobalt and copper. Frequently carries minute quantities of gold (auriferous pyrite).

Colors: Pale brass yellow on fresh surface, tarnishing to a darker shade. Streak: greenish or brownish black.

Hardness: 6.0 to 6.5 (This is unusually hard for a sulphide)

Density: 5.02

Cleavage: The cleavage is imperfect and its fracture conchoidal. The mineral is brittle.  

Crystallography: Isometric: Cubic
The number of forms that have been observed on pyrite crystals is very large. The cube is the most common of these, with the faces usually being  striated, the striae on adjacent faces being perpendicular to each other. Among other types, the octahedron and the dodecahedron are fairly common. Interpenetrating twins are also common.

Luster:. Metallic, Its luster is very brilliant and splendent.

Optics: (Refractive Index):  a = 1.730; b = 1.758; y = 1.838

Composition, Structure and Associated Minerals:
Pyrite, one of the most common of all minerals, is found under a great variety of conditions as crystals, as crystalline aggregates arid as crystalline masses. It occurs under practically all conditions and in all situations. It is easily recognized by its bright yellow color, its brilliant luster and its hardness. With steel it strikes fire, hence its name from the Greek word meaning fire. It is a good conductor of electricity and is strongly thermo-electric.

Pyrite occurs in quartz veins and as grains or crystals embedded in all kinds of rocks. In rocks it usually appears as crystals, but in vein-masses it may appear either as crystals, with other minerals, or as radiating or structureless masses occupying entirely the vein fissures. In slates it often occurs in spheroidal nodules and concretions of various forms, and also as embedded crystals. The mineral is the product of igneous, metamorphic and aqueous processes. Pyrite weathers readily to limonite. In ore bodies near the surface it is oxidized. A portion of the mineral changes to FeSO4 which percolates downward and aids in the concentration of any valuable metals that may be present in small quantity in the ore. Another portion of the iron remains near the surface in the form of limonite. This covering of oxidized material is known as the "gossan" and it is characteristic of all pyrite deposits. Pyrite is often mined as a gold ore, and sometimes for the copper associated with it. Because of the large amount of sulfur present in the mineral it is never used as an iron ore.

Identification and Diagnostics
The mineral is most easily confounded with chalcopyrite, though the difference in hardness easily distinguishes them.  Chalcopyrite may be readily scratched with a knife blade or a file, while pyrite resists both and has a paler color. Pyrite, moreover, contains no copper. Its metallic gold color earns it the common nickname "Fools Gold".  Pyrite is distinguished from gold by its being brittle.

Occurrence, Localities and Origins:
Pyrite is the most common of all the sulphides. It is a common vein mineral, occurring in rocks of all ages and associated with many different minerals. Found frequently with chalcopyrite, sphalerite, galena, etc. Pyrite crystals are so widely distributed that but very few of its most important occurrences may be mentioned here. In the mines of Cornwall, Eng., and in those on the Island of Elba very large crystals are found. Fine crystals also come from many different places in Bohemia, Hungary, Saxony, Peru, Norway, and Sweden. In the United States the finest crystals are at Schoharie and Rossie, N. Y.; at the French Creek mines in Chester Co., and at Cornwall, Lebanon Co., Penn., and near Greensboro and Guilford Co., N. Carolina.

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Pyrite, with Quartz, California Mother Lode

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