Claystone

Rock made mainly of clay minerals: soft, smooth and slick when wet.

Claystone specimen — Photo: James St. John, CC BY 2.0, via Wikimedia Commons

How to identify claystone

Very smooth, soapy when wet.
Scratched by a fingernail.
Swells or slakes in water.

Often confused with

Mudstone
Mudstone contains silt and is a bit harder.
Compare side by side
Kaolinite
Kaolinite is a single white clay mineral.
Compare side by side

Where it's found

Sedimentary basins worldwide

Uses

Ceramics and bricks.

Rock tumbling

Not suitable for tumbling.

Did you know?

Swelling clays in claystone can crack foundations when they get wet.

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