Pyrite 

Pyrite is commonly referred to as “fool’s gold.” Although much lighter than gold, its brassy color and relatively high density misled many novice prospectors. Its name is derived from the Greek word pyr, meaning “fire,” because it emits sparks when struck by iron. It is opaque and pale silvery yellow when fresh, turning darker and tarnishing with exposure to oxygen. Pyrite crystals may be cubic, octahedral, or twelve-sided “pyritohedra,” and are often striated. Pyrite can also be massive or granular, or form either flattened disks or nodules of radiating, elongate crystals. Pyrite occurs in hydrothermal veins, by segregation from magmas, in contact metamorphic rocks, and in sedimentary rocks, such as shale and coal, where it can either fill or replace fossils.

Name: From the Greek for fire, as sparks may be struck from it.

Polymorphism & Series: Dimorphous with marcasite; forms a series with cattierite.

Mineral Group: Pyrite group.

Association: Pyrrhotite, marcasite, galena, sphalerite, arsenopyrite, chalcopyrite, many other sulfides and sulfosalts, hematite, fluorite, quartz, barite, calcite.

Chemical Properties of Pyrite

Physical Properties of Pyrite

Optical Properties of Pyrite

Occurrence of Pyrite 

Formed under a wide variety of conditions. In hydrothermal veins as very large bodies, as magmatic segregations, as an accessory mineral in igneous rocks, in pegmatites; in contact metamorphic deposits, also in metamorphic rocks; as diagenetic replacements in sedimentary rocks.

Uses Area

Pyrite was once used as a source of sulfur, but is now only a minor ore for both sulfur and iron. Pyrite from some localities is auriferous, and therefore is used as an ore of gold in gold-bearing localities. Pyrite was polished by the Native Americans in the early times and used as mirrors. Today, it is used as an ornamental stone, as well as a very popular stone for amateur collectors. It is sometimes used as gemstone by being faceted and polished for use as an inexpensive side gemstone in some rings, necklaces, and bracelets.

Distribution

The most abundant and widespread sulfide. Only a few localities for large or fine crystals can be mentioned. From Rio Marina, on Elba, and at Traversella, Piedmont, Italy. From Ambasaguas and Navajun, Logro˜no Province, Spain, sculptural groups of crystals. At Aktchitao, Kazakhstan. In the USA, in the Ibex mine, Leadville, Lake Co., Colorado; in Illinois, as “suns” at Sparta, Randolph Co.; very large crystals from the Santo Ni˜no mine, near Duquesne, Santa Cruz Co., Arizona. In Pennsylvania, at the French Creek mines, Chester Co., and in the Carleton talc mine, Chester, Windsor Co., Vermont. From Butte, Silver Bow Co., Montana; at the Spruce claim, King Co., Washington; as “bars” from the Buick mine, Bixby, Iron Co., Missouri. In Peru, from many districts, with exceptional crystals from the Quiruvilca mine, La Libertad, and Huanzala, Huanaco.

References

• Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.
• Handbookofmineralogy.org. (2019). Handbook of Mineralogy. [online] Available at: http://www.handbookofmineralogy.org [Accessed 4 Mar. 2019].
• Mindat.org. (2019). Pyrite: Mineral information, data and localities.. Available at: https://www.mindat.org/