What Is Rock? – Types Of Rocks

What is Rock?

A rock is any naturally occurring solid mass coherent aggregate of one or more minerals or mineral-like matter. It may be up to one mineral. i.e.- Monomineralic.

Types of Rocks:

They are categorized by the minerals including their chemical composition and how it is formed.

Rocks are grouped into 3 main categories.

1. Igneous Rock.
2. Sedimentary Rock.
3. Metamorphic Rock.

1. Igneous Rocks:

The rocks that have formed from an originally hot molten material occurring naturally below the surface of the earth (magma) through the process of cooling and crystallization are called igneous rocks. Igneous rocks are further classified into :

• Volcanic Rocks – These are the igneous rocks formed from lava erupted from a volcano, on the surface of the earth by cooling and crystallization.
• Plutonic Rocks – These are igneous rocks formed at considerable depths generally between 7-10 km below the surface of the earth.
• Hypabyssal Rocks – These igneous rocks are formed at intermediate depths, generally up to 2 km below the surface of the earth.

Engineering uses of Igneous Rocks –

They are used for the foundation of dams and reservoirs, as igneous rocks are very strong. Ex- Basalt

2. Sedimentary Rocks:

These rocks are formed from the consolidation of sediments caused due to weathering, erosion, or deposition.

Weathering – It is the breaking down of rocks into sediments.

Erosion – It involves weathering and the transportation of sediments.

Deposition – It is the process when water, wind, ice, or gravity loses energy causing sediments to drop.

Sedimentary rocks are further classified into –

• Clastic – It is formed by compaction and cementation of fragments and is identified by the size of fragments. Ex- Sandstone.
• Non-clastic – It is formed from chemical reactions chiefly in the ocean. Ex- Limestone.

3. Metamorphic Rocks:

Metamorphic rocks are rocks formed from pre-existing rocks, the mineralogy, chemistry, and texture of which have been changed by heat over the period of time or pressure while forming.

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