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Clasts ( Greek κλάω (kláo): to break) are solid fragments of rock that result from the mechanical destruction of other rocks. They range in size from blocks to gravel and sand to silt and clay . Depending on the original rock, the clasts consist of rocks such as granite , gneiss or sandstone and limestone .

Pyroclasts are rock fragments that have arisen from a solid or liquid volcanic starting material through tearing or breaking (fragmentation) or through direct crystallization as a result of volcanic activity.

A special case of clasts are bioclasts that arise from the remains of living beings, so they do not come from the destruction of other rocks and can even consist of unbroken shells or fossils .

Rocks made up of clasts are called clastic or detritic rocks. The term clasts is Gesteinskunde a structural feature .


  • Hans Murawski, Wilhelm Meyer: Geological dictionary . 11th edition. Elsevier / Spektrum, Heidelberg 2004, ISBN 3-8274-1445-8 , pp. 112 .