Igneous rocks are formed by the cooling of hot magma.The grain size of magma depends on the following factors.
1.Rate of cooling:If magma cools rapidly then its molecules do not get enough time to be crystallize. Hence grain size become small.If magma cools slowly then its grain size become big.
2.Molecular concentration:If the magma is of high molecular concentration the every molecule get enough molecules surrounding it for crystallization.Hence grain size become big.If the magma is of low molecular concentration the grain size become small.
3.Viscosity:If viscosity of magma is low its molecules can move freely and get touched with large number of molecules then the magma of high viscosity.Hence the magma of low viscosity make large grain sized igneous rock.
1.Rate of cooling:If magma cools rapidly then its molecules do not get enough time to be crystallize. Hence grain size become small.If magma cools slowly then its grain size become big.
2.Molecular concentration:If the magma is of high molecular concentration the every molecule get enough molecules surrounding it for crystallization.Hence grain size become big.If the magma is of low molecular concentration the grain size become small.
3.Viscosity:If viscosity of magma is low its molecules can move freely and get touched with large number of molecules then the magma of high viscosity.Hence the magma of low viscosity make large grain sized igneous rock.
