The Rock Cycle
Rocks are formed, broken down, and reformed into different types of rocks. The rock cycle shows the relationships among the three major rock types: igneous, sedimentary, and metamorphic.
• Igneous rocks form when molten material cools and hardens.
• Sedimentary rocks form when loose sediments that were previously eroded from existing rocks are lithified.
• Metamorphic rocks form when pre-existing rocks are subjected to heat and pressure.
The Rock Cycle (Drawing by Phyllis Newbill)
Through geologic processes, each type of rock can be re-formed into any of the three types. Note that any rock type can be weathered to become sediment and then a sedimentary rock. Any rock type can also be subjected to heat and pressure and become a metamorphic rock.