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Formula: FeS2
Oxidation states: Fe2+S1-2 (AM 87.1692-1698)
Sulphide, the orthorhombic paramorph of isometric
pyrite, marcasite group
Crystal System: Orthorhombic
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
Environments:
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.
Localities
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).
Marcasite from Thunder Bay - Image
At the Elder mine, Rouyn-Noranda, Quebec, Canada, marcasite epitactic on
pyrite is common
(R&M 96.6.562-565).
At Johanngeorgenstadt, Erzgebirgskreis, Saxony, Germany, marcasite was often found In the ore veins, associated
with proustite-pyraragyrite,
acanthite and native silver, less
often with the cobalt - nickel
arsenides. It was seen in nodular, reniform, shell-like, grape-like and radial
forms, in some cases well crystallised. Attractive specimens showing marcasite on
hematite with galena and
native silver from the Gnade Gottes mine are known
(MinRec 55.5.600).
At Santa Eulalia, Aquiles Serdán Municipality, Chihuahua, Mexico, marcasite pseudomorphs
after pyrrhotite have been found
(R&M 95.3.275).
Marcasite from Santa Eulalia - Image
At Ladywash mine, Eyam, Derbyshire, England, UK, marcasite is associated with baryte
(RES p119).
Marcasite from Ladywash - Image
At Hampstead Farm quarry, Chipping Sodbury, South Gloucestershire, England, UK, marcasite is associated with
calcite and baryte
(RES p173).
Marcasite from the Hampstead Farm quarry -
Image
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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