Rock cycle
The rock cycle describes how rocks form, break down, transform, melt, and reform through geologic time. It connects igneous, sedimentary, and metamorphic rocks through processes such as cooling, weathering, erosion, burial, lithification, metamorphism, uplift, and melting.
What the rock cycle is
The rock cycle is a model for how rocks change through time. It links the three broad rock groups: igneous rocks that crystallize from molten material, sedimentary rocks that form from deposited particles or chemical precipitates, and metamorphic rocks that change in the solid state under heat, pressure, stress, or fluids.
Igneous beginnings
Igneous rock forms when magma or lava cools and solidifies. Slow cooling underground can produce coarse crystals, while rapid cooling at or near the surface usually makes finer-grained volcanic rock. Once exposed, igneous rock can weather into sediment, be buried and metamorphosed, or melt again in a different tectonic setting.
Weathering, erosion, and sediment
At Earthโ€s surface, rock is broken down by weathering. Water, wind, ice, gravity, organisms, and chemical reactions move and alter material. Erosion transports sediment to rivers, lakes, deserts, glaciers, coasts, and ocean basins. These loose particles are the raw material for many sedimentary rocks.
Sedimentary rock formation
Sedimentary rocks form when sediment is deposited, buried, compacted, and cemented, or when minerals precipitate from water. Sandstone, shale, limestone, conglomerate, and evaporite rocks can preserve layers, fossils, ripples, mud cracks, and other clues about ancient environments.
Metamorphic change
Any rock type can become metamorphic if conditions change enough while the rock remains mostly solid. Heat, pressure, deformation, and fluids can recrystallize minerals and create new textures. Slate, schist, gneiss, marble, quartzite, and amphibolite all represent different metamorphic paths.
Melting and recycling
Rocks can melt when temperature rises, pressure drops, or water and other volatiles lower melting conditions. Melting often happens near subduction zones, rifts, hot spots, and parts of the lower crust or mantle. The melt may rise, cool, and become igneous rock, beginning another branch of the cycle.
Plate tectonics as the engine
Plate tectonics gives the rock cycle much of its motion. Uplift exposes deep rocks to weathering. Subduction carries oceanic crust and sediment downward. Mountain building buries and deforms rocks. Spreading centers and volcanoes create new igneous crust. Without plate motion, the cycle would be slower and less varied.
Why it matters
The rock cycle matters because rocks are records of changing environments, tectonic events, climate, life, water, and deep Earth processes. Reading the cycle helps geologists reconstruct landscapes, find resources, understand hazards, and connect surface change with forces deep inside the planet.