Published on 31 Jan 2025
Rocks are aggregates of one or more minerals held together by chemical bonds. Based on the formation they are of three types.
Igneous or primary rocks
These are rocks formed out of solidification of magma and lava. They are unfossiliferous in nature. Granite, gabbro, pegmatite are examples of igneous rocks.
Types of igneous rocks based on the place, cooling time
Plutonic / Intrusive rocks: Formed when magma cools slowly within earth crust. Here mineral grains formed will be large. They assume different forms – batholiths, laccoliths, lapolith, phacoliths, sills, dykes etc.
Example: Granite
Volcanic / Extrusive rocks: Lava cools on the surface of the earth and forms smooth grains with sudden cooling of lava.
Example: Basalt
Sedimentary rocks
They are formed by lithification– the process of consolidation and compaction of sediments. Sedimentary rocks can be layered or stratified with varying thickness. These type of rocks covers 75% of earth’s crust and is fossiliferous in nature. Examples include sandstone, shale etc.
Depending upon formation, it can be of three types
Mechanically formed – Example: conglomerate, loess
Organically formed – Example: geyserite, chalk, coal
Chemically formed – Example: chert, halite, potash
Metamorphic rocks
They are formed by the recrystallization and reorganisation of already consolidated rocks under influence of pressure, volume and temperature. These rocks undergo dynamic metamorphism and thermal metamorphism. Metamorphic rocks includes processes like foliation or lineation and they are also called as banded rocks.
Geography
Rocks and their characteristics
types of rock
Igneous rocks
primary rocks
Sedimentary rocks
metamorphic rock
General Studies Paper 1
Physical Geography
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