Question

How do geologists classify rocks?

Answer 1

Hint: Rocks are naturally occurring solid masses that are made of a mineral or a group of minerals. Different rocks vary from each other on aspects such as mineral and chemical composition, permeability, texture of the constituent particles, and particle size.

Complete answer: Geologists classify rocks into three broad categories- Igneous, metamorphic and sedimentary rocks.
-Igneous rocks are those rocks which are formed by the cooling and crystallization of magma. When magma cools deep inside earth it is called intrusive igneous rocks and these are coarse grained in nature. When magma cools on the surface of earth it is called extrusive igneous rock and is fine grained in nature. Igneous rocks are also known as primary rock.
-Metamorphic rocks are the sedimentary, igneous or other rock which when subjected to heat and pressure change the chemical and physical nature to form new kinds of rock. One kind of metamorphic rock can transform into another kind of metamorphic rock too.
-Sedimentary rocks are those rocks which are formed by the accumulation, cementation and lithification of fragments and sediments of some other rocks which got broken down due to weathering and erosion. These are further classified into clastic, chemical and organic sedimentary rocks.

Note: Granite, diorite are examples of intrusive igneous rock while basalt is an extrusive igneous rock. Quartzite, gneiss and marble are examples of metamorphic rock. Coal is an example of organic sedimentary rock while gypsum is an example of chemical sedimentary rock. Breccia, sandstone and siltstone are examples of clastic sedimentary rock.