The crust of Earth is formed by a variety of rocks differing from each other in composition, texture, color, etc. Among them are sedimentary rocks, that have been weathered into flawless perfection by time itself. Let us learn about all types of sedimentary rocks.

How many types of sedimentary rocks are there?

Sedimentary rocks may be divided into a number of types that depend upon their source, the nature of their sediments, their origin, and their mode of formation.

Types of Sedimentary rocks

On the basis of the character of the material and the process that led to the deposition, there are three types of sedimentary rocks:

1. Mechanically formed Sedimentary Rocks
2. Chemically formed Sedimentary rocks
3. Organically formed Sedimentary rocks.

On the basis of transporting agents such as running water, wind, glaciers, ocean currents, and sea waves, the sedimentary rocks can be categorized as:

1. The Argillaceous Rocks
2. The Aeolian Sedimentary Rocks
3. The Glacial Sedimentary Rocks

Mechanically formed Sedimentary rocks - Alternate name: Stratified Rocks

These rocks are built upon pre-existing rocks and hence contain fragments from breaking up of other rocks, which takes place due to denudation by agents such as running water, moving glaciers, and wind.

Formation: The sediments which are called Clastic sediments, are gradually squeezed by the weight of overlying sediments and the lower layer hardens to form rocks. Since these rocks are formed in layers, they are known as Stratified Rocks.

Basically, these rocks are formed due to the consolidation of gravel, sand, silt, and clay sediments. For example Sand becomes Sandstone. Generally, these rocks are subdivided according to the grain size of their components material.

The Glacial Rocks

The sediments deposited by glaciers are glacial drift which makes up glacial sedimentary rocks.

Formation: These rocks are formed by glacial deposits in the form of debris or tills. The glaciers erode the surface and the sides of a valley and transport the eroded material further. When the Glacier melts, the debris brought by it is left behind in the form of Moraines, which form Glacial rocks.

So basically Morain is an accumulation of material that has been transported or deposited by ice. Moranis is further classified into four types:

• Lateral moraines
• Medial moraines
• Ground moraines
• Terminal moraines

The glacial rocks include boulders, gravels, sand, etc.

The Aeolian Rocks

Sediments deposited after transport by winds are called Aeolian deposits.
Formation: The existing rocks are broken by the agents of mechanical weathering in hot and dry areas. This results in the formation of a large amount of sand. The wind picks up the sand particles and deposited them at various places. Loess deposits are an important example of Aeolian deposits.

The Argillaceous or Aqueous rocks

This is a type of Sedimentary rock that is formed in water bodies. There is a dominance of clay in these rocks. Hence the name aqueous rocks have been given to them.

The Argillaceous rocks are further divided into three types:

The Riverine sedimentary rocks.

These are formed due to the deposition of sediments in the riverine environment. The deposition can take place in the bed of rivers or in the flood plains.

The Lacustrine sedimentary rocks

These are formed due to the deposition and consolidation of sediments in the lake environment. Mostly the sediments are deposited on the floor of the lakes.

The Marine sedimentary rocks

These are formed due to the deposition and consolidation of sediments on the floor of oceans and seas. The size of the particles deposited decreases from coastal areas towards the open oceans and seas.

Read More: Types of Metamorphic Rocks: What are Metamorphic Rocks - Formation