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Question
How are igneous rocks formed?
Solution
Igneous rocks are formed by the cooling and solidification of molten rock called magma, which lies beneath the earth’s crust. These rocks are crystalline and compact. They do not occur in layers or strata nor do they contain fossils.
The cooling and solidification may take place at some depth within the earth or at the surface. The molten magma that reaches the surface of the earth is called lava. Thus, there are two types of igneous rocks classified on the basis of their place of origin – intrusive rocks, which form at some depth in the earth’s crust and extrusive rocks which form at or near the surface of the earth.
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