Rock cycle and Types of rocks Upsc

Rock cycle and Types of rocks

The rock cycle is a continuous process by which the old rocks are transformed into a new one. The changes are caused by various chemical and physical processes. There are three major types of rocks and they are igneous rocks, sedimentary rocks, and metamorphic rocks.


The earth’s crust is made up of rocks and rocks are a mixture of one or more minerals. Rocks can be hard for example granite is hard and soft for example soapstone is soft.

Rocks are found in different colors. For example, Gabbro is black, quartzite is milky white. Also, rocks do not have a definite composition of minerals constituents.

The most common minerals found in the rocks are Feldspar and quartz.

The rocks are directly related to the landforms. This is studied in Petrology, which is studying the science of rocks.

On the basis of their formation, there are different rock types are classified and basically, there are three families of rocks.

  1. Igneous Rocks
  2. Sedimentary Rocks
  3. Metamorphic Rocks

Igneous Rocks

It is formed out of magma and lava. Igneous rocks are called Primary rocks. In Latin language, Ignis means Fire. These rocks are formed when magma cools and solidifies.

This cooling process and solidification process happen in the earth’s crust or earth’s surface. Based on texture, the Igneous rocks are classified. Texture means the size and arrangement of grains and also the physical condition of rock.

If the magma is cooled slowly in the greater depths, the grain size will be large. Rapid cooling of Magma on the surface produces small and smooth grains. Intermediate cooling results in the intermediate size of grains.

Example of Igneous rock is Tuff, volcanic breccia, basalt, pegmatite, gabbro, Granite.

Sedimentary Rocks

It is derived from the Latin word Sedimentum which means settling. The rocks of various types are broken up into fragments of various sizes due to various denudation agents.

Such fragments are transported to exogenous agencies and deposited and these deposits turn rocks by compaction. This process is called Lithification.

The number of layers of varying thickness in sedimentary rocks like sandstone, shale, etc. Sedimentary are classified into three types are Mechanically formed, Organically formed, Chemically formed.

Mechanically formed sedimentary rocks are Sandstone, conglomerate, limestone, shale, loess, etc. Organically formed sedimentary rocks are geyserite, chalk, limestone, coal, etc

Chemically formed sedimentary rocks are chert, limestone, halite, potash, etc.

Metamorphic rocks

Metamorphic means ‘change of form‘. The metamorphic are rocks are formed under the joint action of Pressure, Temperature, and Volume (PVT) changes.

When the rocks are subject to great pressure by the tectonic process or magma in molten states comes in contact with crustal rocks, the underlying rocks applied with great pressure by the overlying rocks, Metamorphism occurs.

Metamorphism is a manner by which previously consolidated rocks are reduced to re-crystallization and rearrangement within original rocks.

A type of metamorphism is Dynamic Metamorphism, which means without any remarkable chemical changes there occurs a mechanical disruption and change of the original minerals within rocks due to breaking and crushing.

Another type of metamorphism is thermal metamorphism and it is classified into two types and they are Contact Metamorphism and Regional Metamorphism.

The rocks come into the contact with hot intruding molten lava or magma and recrystallize under high temperature is called Contact Metamorphism.

The rock materials recrystallize due to the deformation created by tectonics shearing with high temperature or pressure or both. This is Regional metamorphism.

Foliation or lineation is the term used to mention the arrangement of minerals or grains in metamorphic rocks.

Sometimes minerals or materials of various groups are ordered into alternating slim to dense layers looking in light and dark colors, such a formation in metamorphic rocks is called Banding, and rocks exhibiting banding is called Banded rocks.

Metamorphic rocks are divided into two groups, foliated rocks, and non-foliated rocks.

Examples of metamorphic rocks are Gneissoid, granite, syenite, slate, schist, marble, quartzite, etc.

Rocks Cycle

geography optional - Physical geography of rock cycle
Rock Cycle: Physical Geography

Rocks do not remain the same, they transform this called Rock Cycle. Igneous rocks are the primary rocks, metamorphic and sedimentary rocks are other forms of these primary rocks.

The igneous and metamorphic rocks are can be fragmented and turn into sedimentary rocks. Sedimentary rocks also fragment further to become new sedimentary rocks.

The crustal rocks such as Metamorphic and Igneous rocks can sub-duct due to various movement, moves slowly to the mantle and due to high temperature it gets molten down to lava and the rocks cycle continues.


Why igneous rocks are called primary rocks?

  • It is called primary rock because these rocks are formed from the material that comes from below the earth.

  • That is these rocks are formed from the solidification of Magma.

  • Also Igneous rock which directly or indirectly provide materials for the formation of the other types of rocks.

  • Therefor Igneous rocks are also called Mother rocks or Primary rocks.


* * All the Notes in this blog, are referred from Tamil Nadu State Board Books and Samacheer Kalvi Books. Kindly check with the original Tamil Nadu state board books and Ncert Books.