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Claystone identification and geology

Claystone rock reference specimen

Very fine-grained clastic rock composed predominantly of clay-sized particles <0.004 mm . Non-fissile. Texture: Very fine-grained, massive. Rock type: Sedimentary Clastic. Grain size: Clay <0.004 mm. Minerals present: Kaolinite, Illite, Montmorillonite, Quartz. Formation: Forms from deposition and compaction of clay in very low-energy environments. Common geological settings: Worldwide; found in deep marine, lacustrine, and floodplain environments. Common look-alikes and related entries: Mudstone, Shale, Siltstone.

Sources, scope & corrections

These authoritative resources support category-level nomenclature, terminology, identification methods, and safety. When a specimen-specific safety warning appears, the public-health source listed here directly supports that precaution. They are not line-by-line citations for every other property on this entry, and natural specimens vary.

Editorial owner
GeoMiner
Last updated
2026-03-30T14:38:19.618452+00:00
Review status
Published; not independently peer-reviewed
  • Rocks — U.S. National Park Service. Authoritative overview of rock groups, the rock cycle, and geologic processes.
  • Can you identify my rock or mineral? — U.S. Geological Survey. Identification limitations and routes to in-person professional verification.

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Common questions

What is Claystone?
Very fine-grained clastic rock composed predominantly of clay-sized particles <0.004 mm . Non-fissile.
How can you identify Claystone?
Compare several properties rather than relying on colour alone. This entry records rock type: Sedimentary Clastic; texture: Very fine-grained, massive; grain size: Clay <0.004 mm; common minerals: Kaolinite, Illite, Montmorillonite, Quartz. Confirm an important identification with additional field tests or qualified laboratory work.
How does Claystone form?
Forms from deposition and compaction of clay in very low-energy environments.
Where is Claystone commonly found?
Worldwide; found in deep marine, lacustrine, and floodplain environments.
What is Claystone commonly confused with?
Claystone may be confused with Mudstone, Shale, Siltstone. Compare multiple diagnostic properties because colour and surface appearance can overlap.

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