Igneous

rock is that which has been solidified from lava or magma. Igneous is one of three primary classifications of rock, along with metamorphic and sedimentary. The speed at which it cools can determine in part the structure of the rock by varying the amount of crystallization. About ninety per cent of the top portion of the world's crust is made up of igneous rock, however it is hidden by sedimentary and metamorphic layers. Probably the most widely known of the igneous rocks is granite.