The rock cycle

Rocks slowly change from one type to another in the rock cycle, driven by the Sun's energy and the Earth's internal heat. Weathering and erosion break rocks into sediment, which is carried away and deposited in layers. Over millions of years the layers are compacted and cemented into sedimentary rock.

Heat and pressure deep underground can change rock without melting it, making metamorphic rock: mudstone becomes slate and limestone becomes marble. If rock melts it becomes magma. Magma that cools slowly underground forms igneous rock with large crystals, like granite. Lava that cools quickly at the surface forms rock with small crystals, like basalt. Uplift brings rocks back to the surface, and the cycle continues.