Formula: FeS2
Oxidation states: Fe2+S1-2 (AM 87.1692-1698)
Sulphide, the orthorhombic paramorph of isometric pyrite, marcasite group
Specific gravity: 4.887
Hardness: 6 to 6½
Streak: Dark grey to black
Colour: Pale brass-yellow, tin-white on fresh exposures.
Solubility: Insoluble in hydrochloric acid and sulphuric acid
Common impurities: Cu,As

Sedimentary environments
Metamorphic environments
Hydrothermal environments

Marcasite most frequently occurs as replacement deposits also often in concretions and in limestone, and often in concretions and replacing organic matter and forming fossils in sedimentary beds, particularly coal beds. It is also found in chemical sedimentary environments, massive and disseminated hydrothermal replacement deposits and hydrothermal replacement lodes and in epithermal (low temperature) hydrothermal veins.
Marcasite may be found in clay, marl, shale and dolostone.
In hydrothermal veins it may be associated with pyrite.
Marcasite is a mineral of low-temperature, near-surface, environments, forming from acid solutions. Pyrite, the more stable form of FeS2, forms in higher temperatures and lower acidity or alkaline environments.


The Two Mile and Three Mile deposits, Paddy's River, Paddys River District, Australian Capital Territory, Australia, are skarn deposits at the contact between granodiorite and volcanic rocks. marcasite is a supergene sulphide that occurs as a replacement product of pyrrhotite (AJM 22.1.41).

At the Gascoyne River, Carnarvon Shire, Western Australia, Australia, goethite pseudomorphs after marcasite occur as nodules in white, fine-grained chalk along the river (AJM 22.2.5-12).

At the Blue Points mine, Thunder Bay, Ontario, Canada, marcasite has been found with galena, chalcopyrite and quartz (R&M 94.4.325).

At the Elder mine, Rouyn-Noranda, Quebec, Canada, marcasite epitactic on pyrite is common (R&M 96.6.562-565).

At Santa Eulalia, Aquiles Serdán Municipality, Chihuahua, Mexico, marcasite pseudomorphs after pyrrhotite have been found (R&M 95.3.275).

At Ladywash mine, Eyam, Derbyshire, England, UK, marcasite is associated with baryte (RES p119).

At Hampstead Farm quarry, Chipping Sodbury, South Gloucestershire, England, UK, marcasite is associated with calcite and baryte (RES p173).

At Croft Quarry, Croft, Blaby, Leicestershire, England, UK, marcasite occurs as groups and single crystals up to 1 mm that frequently show signs of oxidation, associated with analcime, calcite, chalcopyrite and galena (JRS 20.21).

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