What is Marcasite?
Marcasite turns iron sulfide into architecture. Radiating blades and cockscomb clusters catch light far more dramatically than a massive ore sample, making a well-preserved specimen both decorative and scientifically useful.
Mineralogy and crystal structure
Reference formula: FeS2. Marcasite is the orthorhombic dimorph of pyrite. Its cockscomb and spearhead aggregates are diagnostic collector forms, while its greater instability in humid air means that a beautiful specimen needs careful storage. Marcasite is classified with sulfides and has a orthorhombic crystal system. Typical hardness is 6–6.5 on the Mohs scale and specific gravity is approximately 4.8–4.9.
Colour, lustre and habit
Typical colours include pale brass-yellow, silver-yellow, grey. The usual tabular, cockscomb, radiating habit and metallic lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Marcasite forms in or is associated with low-temperature sedimentary, hydrothermal and carbonate-hosted sulfide environments. Important documented localities include France, the United Kingdom, Germany, Peru, Romania and the United States.
Cockscomb geometry in a brass-yellow sulfide
Marcasite turns iron sulfide into architecture. Radiating blades and cockscomb clusters catch light far more dramatically than a massive ore sample, making a well-preserved specimen both decorative and scientifically useful.
Collecting and care
Keep cool and dry, avoid sealed humid packaging and handle gently; oxidation can produce acidic products and powdery decay.
