clast

geology

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June 24, 2026

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In geology, a clast is a fragment of rock. These fragments are key components of clastic sedimentary rocks, which are formed from the accumulation and cementation of these detrital pieces.123

Clasts can vary in size, from large boulders to fine sand and silt particles. They can be composed of various minerals, such as quartz and feldspar, which have survived weathering and been transported to a depositional site. Additionally, bioclasts are fragments of biological origin, like shell fragments or fossils, that are also found in sedimentary rocks.245

The process of cementation hardens these clastic sediments by precipitating mineral matter in the spaces between the fragments, ultimately forming solid sedimentary rock.3

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sedimentary rock
Textural components
Carbonate clasts include fragments weathered from carbonate source rocks outside the depositional basin (lithoclasts) as well as fragments of carbonate sediment eroded from within the basin almost immediately after it was deposited (intraclasts). Silt- to sand-size particles of microcrystalline calcite or aragonite that lack the internal…
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Carbonate clasts include fragments weathered from carbonate source rocks outside the depositional basin (lithoclasts) as well as fragments of carbonate sediment eroded from within the basin almost immediately after it was deposited (intraclasts). Silt- to sand-size particles of microcrystalline calcite or aragonite that lack the internal…
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sedimentary rock
Conglomerates and breccias
…cement or by a finer-grained clastic matrix. Both contain significant amounts (at least 10 percent) of coarser-than-sand-size clasts. Breccias are consolidated rubble; their clasts are angular or subangular. Conglomerates are consolidated gravel whose clasts are subrounded to rounded. Sometimes the term rudite (or rudaceous) is used to collectively refer to…
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…cement or by a finer-grained clastic matrix. Both contain significant amounts (at least 10 percent) of coarser-than-sand-size clasts. Breccias are consolidated rubble; their clasts are angular or subangular. Conglomerates are consolidated gravel whose clasts are subrounded to rounded. Sometimes the term rudite (or rudaceous) is used to collectively refer to…
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