clastic rock

References

clastic rock

Also known as: clastic sedimentary rock, detrital rock, terrigenous clastic sedimentary rock(Show More)

Written by

The Information Architects of Encyclopaedia Britannica

Last updated

June 24, 2026

Quick Summary

Clastic rocks are a type of sedimentary rock formed from fragments of other rocks that have been transported and deposited, typically in water. These fragments, or clasts, are classified by their size, ranging from large boulders and pebbles in conglomerates and breccias to sand-sized grains in sandstones, and finer materials like silt and clay in mudrocks (shale, siltstone, claystone).12

Clastic rocks often form wedge-shaped deposits adjacent to landmasses, accumulating thick layers over time. Examples include sandstones and shales deposited by rivers and streams. The classification of clastic rocks is based on the size, shape, and arrangement of their constituent grains.32

Summary created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

3 Britannica Sources

Ask Britannica AI about this topic

Britannica doesn't have a full article on this topic, so we've curated a list of our relevant coverage.

sedimentary rock
…and sedimentary rock: (1) terrigenous clastic sedimentary rocks and (2) allochemical and orthochemical sedimentary rocks.
Read More
…and sedimentary rock: (1) terrigenous clastic sedimentary rocks and (2) allochemical and orthochemical sedimentary rocks.
Read More

sedimentary rock
Classification systems
…rocks are recognized: (1) terrigenous clastic sedimentary rocks, (2) carbonates (limestone and dolomite), and (3) noncarbonate chemical sedimentary rocks. Terrigenous clastic sedimentary rocks are composed of the detrital fragments of preexisting rocks and minerals and are conventionally considered to be equivalent to clastic sedimentary rocks in general. Because most of…
Read More
…rocks are recognized: (1) terrigenous clastic sedimentary rocks, (2) carbonates (limestone and dolomite), and (3) noncarbonate chemical sedimentary rocks. Terrigenous clastic sedimentary rocks are composed of the detrital fragments of preexisting rocks and minerals and are conventionally considered to be equivalent to clastic sedimentary rocks in general. Because most of…
Read More

rock
Density
The density of clastic sedimentary rocks increases as the rocks are progressively buried. This is because of the increase of overburden pressure, which causes compaction, and the progressive cementation with age. Both compaction and cementation decrease the porosity.
Read More
The density of clastic sedimentary rocks increases as the rocks are progressively buried. This is because of the increase of overburden pressure, which causes compaction, and the progressive cementation with age. Both compaction and cementation decrease the porosity.
Read More

Permian Period
Sediments in tectonically active regions
…the fossil evidence is from clastic material derived from shallow shelf environments or eroded from older rocks and deposited as deepwater debris fans. Thick deposits—perhaps originally 1 to 3 km (0.6 to 1.9 mi) thick—are known in central Nevada, Idaho, and northward into Canada. Similar deposits occur in the Middle…
Read More
…the fossil evidence is from clastic material derived from shallow shelf environments or eroded from older rocks and deposited as deepwater debris fans. Thick deposits—perhaps originally 1 to 3 km (0.6 to 1.9 mi) thick—are known in central Nevada, Idaho, and northward into Canada. Similar deposits occur in the Middle…
Read More

rock
Types of remanent magnetization
…remanent magnetization) is formed in clastic sediments when fine particles are deposited on the floor of a body of water. Marine sediments, lake sediments, and some clays can acquire DRM. The Earth’s magnetic field aligns the grains, yielding a preferred direction of magnetization.
Read More
…remanent magnetization) is formed in clastic sediments when fine particles are deposited on the floor of a body of water. Marine sediments, lake sediments, and some clays can acquire DRM. The Earth’s magnetic field aligns the grains, yielding a preferred direction of magnetization.
Read More

geology
Sedimentary petrology
…rocks are broadly known as clastic rocks because they consist of distinct particles or clasts. Clastic petrology is concerned with classification, particularly with respect to the mineral composition of fragments or particles, as well as the shapes of particles (angular versus rounded), and the degree of homogeneity of particle sizes.…
Read More
…rocks are broadly known as clastic rocks because they consist of distinct particles or clasts. Clastic petrology is concerned with classification, particularly with respect to the mineral composition of fragments or particles, as well as the shapes of particles (angular versus rounded), and the degree of homogeneity of particle sizes.…
Read More

Silurian Period
Clastic rocks
Clastic rocks, including conglomerates, sandstones, and shales, generally occur in wedge-shaped deposits adjacent to land areas from which terrigenous materials (items derived from the erosion of land) erode under conditions of moderate to high annual rainfall. With steady
Read More
Clastic rocks, including conglomerates, sandstones, and shales, generally occur in wedge-shaped deposits adjacent to land areas from which terrigenous materials (items derived from the erosion of land) erode under conditions of moderate to high annual rainfall. With steady
Read More

sedimentary rock
Texture
…groupings exist for sedimentary rocks: clastic (or fragmental) and nonclastic (essentially crystalline). Noncarbonate chemical sedimentary rocks in large part exhibit crystalline texture, with individual mineral grains forming an interlocking arrangement. Depositional setting is an insignificant factor in both determining crystal size and altering crystalline texture. The size of crystals is…
Read More
…groupings exist for sedimentary rocks: clastic (or fragmental) and nonclastic (essentially crystalline). Noncarbonate chemical sedimentary rocks in large part exhibit crystalline texture, with individual mineral grains forming an interlocking arrangement. Depositional setting is an insignificant factor in both determining crystal size and altering crystalline texture. The size of crystals is…
Read More