Iron sulfide polymorph of pyrite, forming in low-temperature acidic conditions. Unstable and tends to decompose over time. Color: Pale brass-yellow with greenish tinge. Luster: Metallic. Streak: Dark greenish-gray. Cleavage: Poor. Hardness: 6-6.5. Transparency: Opaque. Crystal system: Orthorhombic. Chemical formula: FeS₂. Specific gravity: 4.87-4.92. Formation: Forms at low temperatures in acidic conditions, often in sedimentary rocks like chalk, clay, and limestone. Common geological settings: Worldwide; England chalk cliffs , USA, Czech Republic; found in sedimentary rocks. Common look-alikes and related entries: Pyrite, Arsenopyrite, Chalcopyrite.
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These authoritative resources support category-level nomenclature, terminology, identification methods, and safety. When a specimen-specific safety warning appears, the public-health source listed here directly supports that precaution. They are not line-by-line citations for every other property on this entry, and natural specimens vary.
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Last updated
2026-03-30T14:36:59.174224+00:00
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Published; not independently peer-reviewed
IMA–CNMNC List of Mineral Names — International Mineralogical Association. Official mineral-name, nomenclature, and classification records.
Mineral ID Key — Mineralogical Society of America. Physical-property identification methods, repeat-testing guidance, and limitations.
Iron sulfide polymorph of pyrite, forming in low-temperature acidic conditions. Unstable and tends to decompose over time.
How can you identify Marcasite?
Compare several properties rather than relying on colour alone. This entry records colour: Pale brass-yellow with greenish tinge; lustre: Metallic; streak: Dark greenish-gray; Mohs hardness: 6-6.5; cleavage: Poor; crystal system: Orthorhombic; transparency: Opaque. Confirm an important identification with additional field tests or qualified laboratory work.
How does Marcasite form?
Forms at low temperatures in acidic conditions, often in sedimentary rocks like chalk, clay, and limestone.
Where is Marcasite commonly found?
Worldwide; England chalk cliffs , USA, Czech Republic; found in sedimentary rocks.
What is Marcasite commonly confused with?
Marcasite may be confused with Pyrite, Arsenopyrite, Chalcopyrite. Compare multiple diagnostic properties because colour and surface appearance can overlap.
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