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Clast identification and geology

An individual fragment or grain of rock or mineral produced by the mechanical weathering and erosion of a pre-existing rock. Clasts range in size from clay particles <0.004 mm to boulders 256 mm and are classified by the Wentworth scale. The size, shape, roundness, and composition of clasts provide information about transport distance, energy conditions, and source rock lithology. Field: sedimentology. Example: Well-rounded quartzite clasts in a Cretaceous conglomerate indicate prolonged fluvial transport from a distant source terrane, with softer lithologies eliminated during transport.. Related terms: Clastic, Wentworth scale, Roundness, Sorting.

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
2026-03-30T15:19:41.970235+00:00
Review status
Published; not independently peer-reviewed
  • USGS Thesaurus — U.S. Geological Survey. Controlled earth-science terminology used to describe USGS information resources.
  • Glossary of Geologic Terms — U.S. National Park Service. Geologic definitions prepared by the NPS Geologic Resources Inventory.

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Common questions

What does Clast mean in geology?
An individual fragment or grain of rock or mineral produced by the mechanical weathering and erosion of a pre-existing rock. Clasts range in size from clay particles <0.004 mm to boulders 256 mm and are classified by the Wentworth scale. The size, shape, roundness, and composition of clasts provide information about transport distance, energy conditions, and source rock lithology.
What is an example of Clast?
Well-rounded quartzite clasts in a Cretaceous conglomerate indicate prolonged fluvial transport from a distant source terrane, with softer lithologies eliminated during transport.
Which earth-science field uses the term Clast?
Clast is used in sedimentology.
Which terms are related to Clast?
Related terms in this reference are Clastic, Wentworth scale, Roundness, Sorting.

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