Igneous rocks solidify from molten rock. They are identified by mineral content and texture the size and shape of their mineral grains. Both sedimentary and metamorphic rocks can get so hot they turn into liquid rock (magma). The liquid surface rock (lava) solidifies to form igneous rock. The magma bursts through Earth's surface in the form of a volcano. Heat and pressure deep in the Earth makes some rocks change to metamorphic rock.