Rocks are formed on Earth as igneous, sedimentary, or metamorphic rocks.
Igneous rocks form when rocks are heated to the melting point which forms magma.
Metamorphic rocks form from heat and pressure changing the original or parent rock into a completely new rock. The parent rock can be either sedimentary, igneous, or even another metamorphic rock. The diagram above shows you how the rocks on Earth have been changed continually over time from one rock type to another.