A mountain crumbles to sand, the sand hardens to rock, that rock melts and cools into new rock — over millions of years the same material keeps changing form. The rock cycle is Earth's endless recycling program.
Three kinds, one cycle
Igneous rock forms when magma cools. Sedimentary rock forms when eroded bits are pressed and cemented in layers. Metamorphic rock forms when heat and pressure change existing rock without melting it. Given enough time, any rock can become any other.
Heat from Earth's interior and weathering at the surface drive the cycle — melting, cooling, eroding, compacting, and cooking rock over millions of years.
- Lava cools on a volcano's slope — what rock type forms?
- Sand is buried and cemented over ages — what type?
- Deep burial cooks limestone into marble — what type?
What you should see: Cooling magma → igneous; compacted sediment → sedimentary; heat-and-pressure change → metamorphic. Each is a stage of one continuous cycle.