Marcasite

Same chemistry as pyrite but a different crystal structure; paler and more prone to crumbling.

Marcasite specimen — Photo: Didier Descouens, CC BY-SA 4.0, via Wikimedia Commons

How to identify marcasite

Pale brass to tin-white, often in spear or cockscomb shapes.
Nodules in chalk with radiating insides.
May crumble to white powder in humid storage.

Often confused with

Pyrite
Pyrite is yellower and forms cubes.
Compare side by side
Arsenopyrite
Arsenopyrite smells of garlic when struck.
Compare side by side

Where it's found

Chalk cliffs of Dover, England
Bohemia, Czech Republic
Tri-State district, USA

Uses

Collector specimens.

Rock tumbling

Not suitable for tumbling. Decays easily and releases sulfuric acid.

Did you know?

Vintage 'marcasite' jewelry is almost always set with pyrite, not marcasite.

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