Claystone is a fine-grained, non-fissile sedimentary rock composed primarily of clay-sized particles. Unlike shale, it does not display fissility or splitting along thin parallel laminations and often feels smooth or powdery to the touch when dry.
Is this claystone?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch claystone with a known reference. Claystone sits at Mohs 1-2, softer than the next harder reference, harder than the previous one.
- 2Read the textureLook at a fresh break with a hand lens. Texture: Non-fissile. Grain size: Particles under 0.0625 mm, less than a third of them silt.
- 3Pick out the mineralsComposition: Mostly clay-sized particles. Identify the two or three most abundant grains.
- 4Read the lusterHold the specimen under a strong light. Luster: dull.
- 5Match the color rangeCompare against the expected color range: gray, brown, red, yellow, black.
Often confused with
Claystone vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside claystone
Minerals reported to co-occur with claystone. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Mohs hardness
- 1-2
- Density
- 2.0-2.6 g/cm³
- Luster
- Dull
- Transparency
- Opaque
- Rarity
- Common
- Uses
- Industrial, Geological study
- Host rock
- sedimentary basins
- Texture
- Non-fissile
- Grain size
- Particles under 0.0625 mm, less than a third of them silt
- Composition
- Mostly clay-sized particles
Where rockhounds find claystone
Classic worldwide localities
- Worldwide
- Kentucky, USA
- London Basin, UK
- Paris Basin, France
Field-hunting tip
Where it forms: sedimentary basins. If you start seeing quartz, feldspar, calcite in float, you are in the right ground.
More claystone photos
Common questions
How do you identify claystone?+
Where is claystone found?+
What rocks look like claystone?+
What minerals are found with claystone?+
What kind of rock does claystone form in?+
What is claystone used for?+
Find claystone on the map
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