Question.
How are extrusive and intrusive rocks formed?
( Chapter - 2 Inside Our Earth, Class 7 NCERT, Our Environment( Geography) )
Answer.
Extrusive and intrusive rocks are kinds of igneous rock ( primary rock) that are formed from hot molten magma.
Formation of extrusive rocks:
Extrusive rocks are formed when molten magma through volcanic eruption comes up on the earth's surface and cools. Basalt rocks of the Deccan plateau are examples of extrusive rocks which is one type of igneous rock.
As molten magma cools on the earth's surface quickly so they have a very fine grains structure. Black soils have very finer particles as they are made up of basalt rocks which are one kind of extrusive rock.
Formation of intrusive rocks:
Intrusive rocks are formed when molten magma cools inside the earth's crust[ in some depth]. Granite rock is an example of intrusive rock which is one kind of igneous rock.
Molten magma cools very slowly inside the earth's crust, so large grain structures develop in the intrusive.
Grinding stones are generally made up of intrusive rock( granite).
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