The Classification of Sedimentary Rocks

Sedimentary rocks refer to rocks that are formed through the deposition of sediments known as the process of sedimentation. Natural phenomenon like weathering and erosion also contributes to the formation of sedimentary rocks.

Thus, scientists and researchers often used sedimentary rocks to figure out how the Earth’s climate changes as time goes by. Fossils and similar historical artifacts and relics are also preserved sometimes in sedimentary rocks.

Sedimentary rocks can be divided based on their genetic make up and formation. Basically, there are four categorization of sedimentary rocks; clastic sedimentary rocks, biochemical sedimentary rocks, chemical sedimentary rocks and the general classification “other sedimentary rocks.”

Clastic sedimentary rocks

Clastic sedimentary rocks or just clastic rocks are rocks usually composed of small fragments of another existing rock. Clastic rocks are transported by water and are deposited once water came to rest. Some examples of clastic rocks include quartz, feldspar, mica and other clay minerals.

Clastic rocks are subdivided into three broad categories based mainly on their clast shape, their composition and their size and texture.

Conglomerates and breccias are clastic sedimentary rocks which are notable for its clast shape while sandstones and mudrocks are the classifications based on their composition and their size and texture respectively.

Conglomerates and breccias are of angular and rounded gravel. Sandstones are known for its abundance of muddy matrix between sand grains. On the other hand, mudrocks are clastic sedimentary rocks displaying fine texture.

Mudrocks are predominantly made up of mud.

Biochemical sedimentary rocks

Biochemical sedimentary rocks are types of sedimentary rocks that are formed through biological processes.  Most of the time, biochemical sedimentary rocks are formed when an organism mixes small materials and particles dissolved in air and water.

Some of the most common types of biochemical sedimentary rocks include biochemical limestone, diatomite, chert and coal.

Biochemical limestone are limestone rich in calcium carbonate. Biochemical limestone are usually formed from remains of marine organisms. Diatomite and chert are dominantly made up of skeletons. Lastly, coals come from concentrated plant matter.

Chemical sedimentary rocks

Unlike the other forms of sedimentary rocks, chemical sedimentary rocks are not made up of sediments. Instead, chemical sedimentary rocks came from mineral crystals dissolved into water. The primary deposition and formation place of chemical sedimentary rocks are oceans and seafloors which are full of dissolved elements from marine organisms.

Common types of chemical sedimentary rocks include oolitic limestone and other rocks made up of evaporative materials.

Other sedimentary rocks

The fourth general categorization of sedimentary rocks are sedimentary rocks made up of volcanic and similar processes.