Sedimentary rocks

Sedimentary Rocks

Sedimentary Rocks

Sedimentary rocks are the most commonplace rock kinds which might be freely uncovered in the world’s floor. They are shaped from other rock substances for the reason that they may be made up from the buildup of weathered and eroded pre-present rocks. The weathering, erosion and the eventual compaction of igneous, metamorphic or previously dependent sedimentary rocks amongst different biological sedimentations ends in the formation of sedimentary rocks. So, Those are constructed from previous rocks which might be relentlessly weathered or eroded and then deposited in which they go through compaction and cementation via a method called lithification- converting of sediments into a rock. This is how the name sedimentary rock changed into coined.


All rocks, be it igneous, metamorphic, or the already existing sedimentary rocks are constantly subjected to weathering and erosion. Tiny debris from the rock masses and mountains are eroded collectively with soils, sand, and different granite portions are commonly washed from highlands to low areas. After a few years, those materials ultimately relax thru the technique of sedimentation. Some can also collect under water and others at the decrease regions of the land.

The weathering and erosion is generally due to the forces of water, thermal growth, gravity, wind, and salt crystal expansion that breaks down the pre-existing rocks into small portions after which carried away to far low areas. As the substances flow, they’re smoothened and rounded by abrasion.

At this point, they’re deposited a layer after layer to form a brand new sheet of homogenous cloth. From right here, the compaction and cementing dealers including oxides, carbonates, and silica integrate collectively with the deposited cloth.

The compaction impact due to the weight of the piling layers of materials reduces the porosity of the rocks shaped and intensifies the concord among the grains. At times, fossil fuels and natural rely may additionally settle within the sediments leading to cementation. Cementation is the gluing of the rock portions together either through salt compounds or natural count. When those materials eventually harden, the aggregate is transformed into a rock.

Thus, sedimentary rocks are fashioned from sediment deposits via the technique of weathering, erosion, deposition and eventually compaction and cementation. Examples of sedimentary rocks include mudstone, limestone, sandstone, and conglomerate.


Sedimentary rocks are of three basic types. These include clastic, chemical, and organic sedimentary rocks.

Clastic Sedimentary Rocks

Clastic sedimentary rocks are formed from the buildup of clatics: small pieces of fragmented rocks deposited as a result of mechanical weathering then lithified by compaction and cementation. Examples of Clastic sedimentary rocks include sandstone, shale, siltstone, and breccias.

Clast size in clastic rocks
Name Grade Size range (mm) Comments
Boulder > 200 Clasts should be identifiable.
Gravel Very coarse 60 – 200
Coarse 20 – 60
Medium 6 – 20
Fine 2 – 6
Sand Coarse 0.6 – 2 Clasts visible to the naked eye. Grains often identifiable.
Medium 0.2 – 0.6
Fine 0.06 – 0.2
Mud < 0.002 – 0.06 Clasts not visible to the naked eye. Feels smooth.

Non-clastic sedimentary rocks

Chemical Sedimentary Rocks

 Chemical sedimentary rocks are formed when the water components evaporate, leaving dissolved minerals behind. Sedimentary rocks of these kinds are very common in arid lands such as the deposits of salts and gypsum. Examples include rock salt, dolomites, flint, iron ore, chert, and some limestone.

Organic Sedimentary Rocks

Organic sedimentary rocks are formed from the accumulation of any animal or plant debris such as shells and bones. These plant and animal debris have calcium minerals in them that pile on the sea floor over time to form organic sedimentary rocks. Examples include rocks such as coal, some limestone, and some dolomites.