Chemical Composition: FeS2
Mohs' Hardness: 6-6.5
Specific Gravity: 5.0-5.2
Cleavage: None
Refractive Index: Over 1.81
Double Refraction: None
Dispersion: None

Pyrite is commonly called Fool's gold for a reason. The metallic mineral is usally a gold/brassy color, and often resembles real gold. However, when struck with a hammer, pyrite will not flatten like the more malleable gold. If struck directly, pyrite will break, as it is rather brittle. If the blow was a glancing blow, pyrite will emit a spark and a sulfurous smell. Pyrite is also commonly mistaken for marcasite. Even though the two stones have the same chemical composition, pyrite forms with a different crystalline structure. Pyrite crystals are shaped as cubes, octahedrons or pyritohedrons, a dodecahedron with pentagonal faces. The name, pyrite, comes from the Greek word for fire, pyr.

While not the best source of iron, Pyrite is considered an important source of sulfur, after native sulfur of course. In WWII, North American sulfur mines were drying up. Pyrite, along with other sulfides like pyrrhotite and pentlandite were mined for their sulfur. This sulfur was used to make sulfuric acid. Nowadays sulfur is culled from H2S gas recovered from natural gas wells.

The Incas used pyrite for use as a mosiac mirror. The mirror consisted of several cubes of pyrite stacked together in close quarters. The reflection was due to the bright metallic lustre of the stone. The largest of these mirrors found has a diameter of 14 centimeters. Before the 18th century, pyrite was very valuable in France. It was used ornimentally on several objects from snuff boxes and shoe buckles to bracelets and brooches. However, it quickly fell out of favor at the turn of the century. An attempt to rekindle France's love for pyrite was attempted inthe 1820's. It was successful for a short while, but then quickly fell out of favor again.

Pyrite can be found in a wide variety of geological formations from sedimentary deposits to hydrothermal veins. Pyrite can even be found as a constituent of metamorphic rocks. Because of the diverseness of sources in which pyrite can be found, veins are known all over the globe. It is one of the most common minerals in the world. Spain, Tuscany, Norway, Sweden, Germany, Russia, Arizona and Pennsylvania all have large pyrite veins.


Sources:
Precious Stones, by Dr. Max Bauer. Charles E. Tuttle Company: Rutland Vermont and Tokyo, Japan, 1969
Gemstones of the World, by Walter Schumann. Sterling Publishing Co., New York, 1979
Simon and Schuster's guide to Rocks and Minerals, Simon and Schuster Inc. New York, 1978
http://mineral.galleries.com/minerals/sulfides/pyrite/pyrite.htm
http://www.chem.ox.ac.uk/mom/pyrite/pyrite.html
Olmec Mirrors: An example of archeological American Mirrors, Jose J. Lunazzi. www.geocities.com/prof_lunazzi/Olmecas/Olmecas_ICO.pdf

Pyr"ite (?), n.; pl. Pyrites (#). [Cf. F. pyrite. See Pyrites.] Min.

A common mineral of a pale brass-yellow color and brilliant metallic luster, crystallizing in the isometric system; iron pyrites; iron disulphide.

Hence sable coal his massy couch extends, And stars of gold the sparkling pyrite blends. E. Darwin.

 

© Webster 1913.

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