Anhydrite

Calcium sulfate without water — gypsum's dry cousin, forming in salt deposits.

Anhydrite specimen — Photo: Alcinoe, Public domain, via Wikimedia Commons

How to identify anhydrite

Breaks into blocks along three cleavages at right angles.
Harder than gypsum.
Doesn't fizz in acid.

Often confused with

Gypsum
Gypsum is softer — a fingernail scratches it.
Compare side by side
Calcite
Calcite fizzes and cleaves into slanted rhombs.
Compare side by side

Where it's found

Naica, Mexico
Peru
Germany
Poland

Uses

Cement additive and plaster.

Rock tumbling

Can be tumbled with care.

Did you know?

Pale blue 'angelite' sold in crystal shops is anhydrite from Peru.

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