Report Abuse. Igneous rocks are crystalline solids which form directly from the cooling of magma.The chemistry of the parent rock largely determines the composition of the resulting metamorphic rock. So the major difference is that Igneous rocks are made from magna and metamorphic rock is made from any other rock.hen magma appears above the earth, it is called lava. Igneous rocks are formed as the lava cools above ground. Metamorphic rocks are rocks that have morphed into another kind of rock.