The rock cycle shows how the three main rock types - igneous, sedimentary, and metamorphic - are interrelated and constantly transforming into one another over geological time through various natural processes. Igneous rocks form from the cooling of magma, sedimentary rocks form through the lithification of sediments, and metamorphic rocks form under high heat and pressure which causes changes to pre-existing rocks. Rocks are constantly being recycled and transformed as they move through the rock cycle.