Bournonite

A lead copper antimony sulfide whose twinned crystals look like cogwheels.

Bournonite specimen — Photo: CarlesMillan, CC BY-SA 4.0, via Wikimedia Commons

How to identify bournonite

Steel-gray crystals twinned into gear-like shapes.
Metallic and heavy.
Soft — a knife scratches it.

Often confused with

Tetrahedrite
Tetrahedrite forms tetrahedrons.
Compare side by side
Galena
Galena forms cubes and cleaves perfectly.
Compare side by side

Where it's found

Cornwall, England
Hunan, China
Bolivia
Peru

Uses

Minor ore of lead, copper and antimony.

Rock tumbling

Not suitable for tumbling.

Did you know?

Miners called it 'cogwheel ore' for its notched twin crystals.

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