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Iron sulfide mineral that forms pale bronze-yellow crystals; the name cockscomb marcasite refers to the shape of a common form of its crystals. Marcasite has the same chemical formula as pyrite (FeS) but a different internal (atomic) structure. It is less stable than pyrite, being easily decomposed, and is much less common.
This entry comes from Encyclopædia Britannica Concise. For the full entry on marcasite, visit Britannica.com.