The Rock Cycle (detailed) — free printable diagram

What the rock cycle diagram shows

The rock cycle is the set of processes that turn rock from one of the three types — igneous, sedimentary and metamorphic — into another, over and over. The diagram is drawn as a circle because the cycle has no start and no end: any rock type can become any other, given the right conditions and enough time.

Rock types

Igneous, sedimentary, metamorphic

Molten rock

Magma (underground), lava (at the surface)

Makes igneous rock

Cooling and crystallisation

Makes sedimentary rock

Weathering, erosion, compaction, cementation

Makes metamorphic rock

Heat and pressure

Returns rock to magma

Melting

• Igneous rock forms when magma or lava cools and crystallises — quickly at the surface, giving small crystals as in basalt, or slowly underground, giving large crystals as in granite.
• Weathering and erosion break exposed rock into sediment. The sediment is transported, deposited in layers, then compacted and cemented into sedimentary rock such as sandstone or limestone.
• Heat and pressure change an existing rock into metamorphic rock — limestone into marble, shale into slate — without it melting. That distinction is the one students most often lose: melting takes rock out of the solid part of the cycle altogether.
• If rock is buried deep enough and gets hot enough it melts back into magma, and the cycle begins again.
• There is no fixed order. A sedimentary rock can be uplifted and weathered straight back into sediment without ever becoming metamorphic, so tracing several different routes around the diagram makes a good classroom task.
• The processes run on geological timescales — typically thousands to many millions of years — which is why the cycle is modelled rather than observed.