Chalcanthite

Water-soluble copper sulfate. Natural crusts form on mine walls; big blue crystals in shops are lab-grown.

Chalcanthite specimen — Photo: Didier Descouens, CC BY-SA 3.0, via Wikimedia Commons

How to identify chalcanthite

Vivid sky to royal blue.
Dissolves in water.
Turns white and powdery when it dries out.

Often confused with

Azurite
Azurite is darker blue, doesn't dissolve and fizzes in acid.
Compare side by side

Where it's found

Chuquicamata, Chile
Arizona
Spain

Uses

Copper ore; copper sulfate is used as a fungicide.

Rock tumbling

Not suitable for tumbling. Toxic and water-soluble.

Did you know?

Most large chalcanthite crystals for sale were grown in a jar.

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