Process diagram: The rock cycle

The diagram shows how rocks are formed and transformed over millions of years in the rock cycle.

Overall, the cycle has nine stages and is continuous, since the igneous rock that forms at the end can itself be broken down by weathering, which begins the cycle again.

The cycle can be described as starting with weathering, when rock is broken down by wind and water. The resulting fragments are then carried away by rivers and ice in a process called erosion. They are subsequently deposited as sediment, which settles in layers on the sea bed. Under their own weight, these layers are pressed together during compaction, and sedimentary rock such as sandstone is formed when cementing occurs.

At a later stage, the rock is buried deep underground, where it is changed by heat and pressure. Metamorphic rock, such as marble, is formed as a result.

If the temperature continues to rise, extreme heat turns the rock into magma. Finally, the magma cools and solidifies into igneous rock, and the cycle can begin once more.