Andalusite

An aluminum silicate of metamorphic rocks. Its variety chiastolite shows a dark cross in cross-section.

Andalusite specimen — Photo: Ivar Leidus, CC BY-SA 4.0, via Wikimedia Commons

How to identify andalusite

Square prisms, often with a black cross inside (chiastolite).
Gems flash green and red-brown from different angles.
Hardness about 7.

Often confused with

Staurolite
Staurolite crystals cross each other on the outside, not inside.
Compare side by side
Sillimanite
Sillimanite is fibrous.
Compare side by side

Where it's found

Andalusia, Spain
Minas Gerais, Brazil
Sri Lanka
China

Uses

Refractory ceramics, spark plugs and gems.

Rock tumbling

Great for tumbling.

Did you know?

Chiastolite 'cross stones' have long been worn as good-luck charms.

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