Nature · Earth Science
How the three rock families endlessly renew
Rocks are not permanent. Over immense spans of time, every rock is broken down, transported, buried, melted and reborn as another kind of rock. This grand recycling — the rock cycle — links the three great rock families, igneous, sedimentary and metamorphic, in a loop driven by Earth’s internal heat and the weather at its surface.
Molten rock cools into igneous rock; weathering breaks it into sediment that hardens into sedimentary rock; heat and pressure transform buried rock into metamorphic rock; and deeper burial melts it back into magma. Any rock can follow many paths through this cycle, over millions of years.
Melting, cooling, weathering, burial and metamorphism convert each rock family into the others, again and again.
Born from fire
Igneous rock forms as magma or lava cools and crystallises. Cooling slowly underground grows big crystals (granite); cooling fast at the surface makes fine-grained rock (basalt).
Built layer by layer
Weathered fragments and shells settle, pile up and cement together into sedimentary rock. Their layers record time and often preserve fossils — the pages of Earth’s history book.
Transformed by heat and pressure
When rock is buried and squeezed or baked — but not melted — its minerals recrystallise into tougher, often banded metamorphic rock. Limestone becomes marble; shale becomes slate.
Back to the beginning
Dragged deep enough by tectonics, any rock melts back into magma — the molten reset button of the rock cycle. Rising magma then cools into fresh igneous rock and the loop begins anew.