Clastic rock

type of sedimentary rock
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Clastic rocks are composed of fragments, or clasts, of pre-existing rock.

Breccia. Notice the angular nature of the large clasts
Marble breccia from Naples.

Although, in principle, almost any rock made of eroded former rock is clastic (such as sandstone or mudstone), in practice the term is used for clasts of at least gravel size upwards. That means clasts are at least visible to the naked eye, and may be huge.

There are two types of clastic rock, by shape. conglomerates have rounded clasts, and breccias have jagged clasts.[1]

In a clastic rock, the clasts are often of a different make-up from the ground rock or matrix.


  1. Neuendorf, Klaus; Mehl, James; Jackson, Julia 2005. Glossary of Geology. 5th ed, American Geological Institute: Alexandria, VA.