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Gemstones 250x250

The Mineral pyrite

Twinned Pyrite Cubes

Pyrite is sometimes called Fools Gold because of its similarity in color and shape to Gold. In the old mining days, Pyrite was sometimes mistaken for Gold, as they frequently occur together, although Gold and Pyrite can very easily be distinguished by simple observation and testing of characteristics.

Pyrite occurs in numerous shapes and habits. The smaller crystal aggregates may give off a beautiful glistening effect in light, and the larger crystals may be perfectly formed, including fascinating cubes, penetration twins, and other interesting crystal forms. The perfect cubes of Pyrite embedded in a matrix from the famous Spanish mines are especially treasured among collectors. Many of these specimens have fallen out of the matrix and have been repaired by having them glued back into the matrix.

Pyrite has the same chemical formula as the rarer mineral Marcasite, but it crystallizes in a different crystal system, thereby classifying it as a separate mineral species. Aggregates of iron sulfide (FeS2) where the crystal structure cannot be determined without complex analyzing material may be wrongly labeled by dealers. Some Pyrite specimens are labeled as Marcasite, and some Marcasite specimens as Pyrite.


For additional information, see the gemstone section on Pyrite.

Chemical Formula

FeS2

Color

Yellowish gray to gray. Some specimens oxidize and form a yellow-brown or iridescent film on exposed crystal faces.

Crystal System

Isometric

Properties

Streak
Black with a slightly green tinge
Hardness
6 - 6.5
Transparency
Opaque
Specific Gravity
4.9 - 5.2
Luster
Metallic
Cleavage
None
Fracture
Conchoidal
Tenacity
Brittle
Other ID Marks
Some specimens develop a yellow-brown film on crystal faces.

Crystal Habits

Pyrite can form in extremely well-crystallized examples of cubes, pyritohedrons, and octahedrons. Combinations of these forms also occur. An icosahedron formed from a combination of an octahedron and pyritohedron is also known. Pyrite crystals frequently form penetration twinning, especially in the cubic form. Cubes are sometimes elongated in rectangular form. Also occurs massive, radiating, grainy, flaky, drusy, mammilary, encrusting, nodular, tuberose, fibrous, in concretions, and as groups of small crystals. Pyrite crystals are frequently striated

3D Crystal Atlas

Additional Information

Composition
Iron sulfide, sometimes containing small amounts of cobalt, nickel, silver, and gold
In Group
Sulfides; Simple Sulfides
Striking Features
Hardness, color, well shaped crystals, heaviness, and streak
Environment
Pyrite forms in all types of environments.
Rock Type
Igneous, Sedimentary, Metamorphic

Other Names

Fools Gold

Varieties

 -   Pyrite with etched, gothiclike markings
 -   Flat disc of radiating Pyrite or Marcasite.
 -   Large, undistorted, cubic shaped Pyrite.
 -   Synonym of Pyrite Dollar.
 -   Pyrite with with a pyritohedral shape.
 -   Iridescent Pyrite from the Volga River of Russia. Rainbow Pyrite is usually in spherical concretions that contain internal shrinkage fractures, and the iridescence is caused by oxidation.

Uses

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.

Noteworthy Localities

Pyrite is an extremely common mineral, and good examples occur in numerous localities throughout the world. Only well-known localities are mentioned here.

Enormous deposits of Pyrite in the form of small crystal clusters exist in the Huaron Mining District in Peru. Other outstanding Peruvian localities are the Quiruvilca Mine, La Libertad; and the Huanzala, Huánuco. Most of the amateur collector Pyrite comes from the Peruvian locations in abundance, though fine outstanding crystals have also come from there as well.

In the Ampliación a Victoria Mine, Navajún, La Rioja, (formerly Logroño), Spain, large perfect cubic Pyrite crystals, are mined in abundance. They are frequently embedded in a light brown matrix, and are occasionally inter-penetrating. Excellent pyritohedral crystals occur in Rio Marina on the island of Elba, Italy, which is a classic locality. A locality which has recently brought interestingly shaped, complex Pyrite crystals to the market is the Merelani Hills, Arusha, Tanzania.

In the U.S., fine Pyrite localities abound. In Park City, Bingham Co., Utah, large, well shaped pyritohedrons and cubes were once found. The Bingham Canyon Mine, Salt Lake Co., Utah is also a classic occurrence, where few of the excellent Pyrites from the mine are saved from the mining crusher. Large, intergrown cubes, many times partially octahedral, occurred in abundance at Leadville, Lake Co., Colorado. Pyrite "dollars" are well-known from Sparta, Randolph Co., Illinois. The French Creek Mine in Chester Co., Pennsylvania is famous for the octahedral crystals that occur there, although most are distorted. Ross Co., Ohio, produces rounded tubular growths of Pyrite, some reaching several feet in size, as well as growths of spiky, pineapple-like crystals.

Distingushing Similar Minerals

Chalcopyrite - Lower hardness, has a more intense yellow color.
Cobaltite - Lacks yellow color of Pyrite, lower hardness.
Marcasite - Crystallizes in different crystal system.
Pyrrhotite - Lower hardness, darker color, different crystal form.

Small, gold colored, massive or flaky Pyrite may be confused with Gold, but is easily distinguished by Pyrite's black streak and Gold's yellow streak (and by Gold's low hardness and lack of brittleness.)


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