Rock Topics

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.

Rock CycleThe 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.