Pyrite: Fool's Gold

Pyrite is an iron sulfide with the chemical formula FeS2 (iron(II) disulfide). Pyrite is considered the most common of the sulfide minerals.

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. 

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.

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.

Pyrite: Fool's Gold
Pyrite: Fool's Gold. Cubic Crystals of Pyrite Nestled Within a Matrix of Rhodochrosite. From Cassandra Mines,macedonia Dept, Greece

Pyrite is usually found associated with other sulfides or oxides in quartz veins, sedimentary rock, and metamorphic rock, as well as in coal beds and as a replacement mineral in fossils, but has also been identified in the sclerites of scaly-foot gastropods.

Despite being nicknamed fool's gold, pyrite is sometimes found in association with small quantities of gold.

Pyrite is quite easy to distinguish from gold: pyrite is much lighter, but harder than gold and cannot be scratched with a fingernail or pocket knife.

Pyritization: Organisms may become pyritized when they are in marine sediments saturated with iron sulfides. As organic matter decays it releases sulfide which reacts with dissolved iron in the surrounding waters. Pyrite replaces carbonate shell material due to an undersaturation of carbonate in the surrounding waters.

Pyrite Distinctive Characteristics

  • Metallic luster: Pyrite's shiny, metallic appearance is its most recognizable feature, often leading to mistaken identity as gold.
  • Hardness: Pyrite is harder than most other yellow minerals, making it scratch glass and leave a black streak.
  • Cubic crystals: Pyrite's characteristic cubic or octahedral crystals are another telltale sign.
  • Fool's gold: While the resemblance to gold is uncanny, pyrite lacks the malleability and ductility of the precious metal.

Pyrite: Interesting Facts About  Fool's Gold
This is an excellent example of two intergrown cubes of pyrite. from Navaj├║n, La Rioja, Spain
Photo Mardani Fine Minerals
Large Size Natural Pyritized Ammonite Fossils from Russia.
Their Chambers are filled with druzy Pyrite!!
Photo credit: Daniel Virgadaula

Pyrite Properties

  • Chemical Formula: FeS₂ (Iron disulfide)
  • Crystal System: Cubic
  • Color: Pale brassy yellow, sometimes with a greenish or pinkish tinge
  • Luster: Metallic
  • Hardness: 6-6.5 on the Mohs scale (can scratch glass)
  • Streak: Black, often with a green tinge
  • Cleavage: None
  • Fracture: Conchoidal (shell-like)
  • Density: 4.8-5.0 g/cm³ (relatively heavy)
  • Magnetism: Weakly magnetic
  • Other properties: Pyrite is brittle and can be tarnished by moisture or harsh chemicals.
Pyrite ammonite
Pyritized ammonite. From Saratov Russia. Upper Callovian (around 162 million years).
Photo: Leah Luten
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