What is the Rock Cycle describes the natural transformation of one type of rock into others. Beginning with igneous rocks made in volcanic eruptions, rock is weathered and eroded gradually to form a sediment. This sediment is then deposited and pressed into layers making sedimentary rocks. These in turn are transformed by heat and pressure into metamorphic rocks. Heat makes these melt into magma which, together with molten rock from the core of the Earth, make new igneous rocks.