What is the rock cycle?

The rock cycle describes how Earth's rocks continually transform. Three rock types: (1) IGNEOUS — formed when molten rock (magma below ground, lava above) cools and solidifies. Intrusive igneous rocks cool slowly underground (granite, gabbro); extrusive cool quickly above (basalt, obsidian, pumice). (2) SEDIMENTARY — formed from accumulated sediments (weathered rock fragments, organic material, mineral precipitates) compressed and cemented over time. Examples: sandstone, limestone, shale, coal. Often layered and may contain fossils. (3) METAMORPHIC — formed when existing rocks are altered by heat, pressure, or chemical activity without melting. Examples: marble (from limestone), slate (from shale), gneiss (from granite or sedimentary), quartzite (from sandstone). Rock cycle transformations: igneous can weather/erode to sediment → sedimentary; sedimentary can be buried and metamorphosed → metamorphic; metamorphic can be uplifted and weathered → sediment → sedimentary; any rock can melt → magma → cool → igneous. Driving forces: plate tectonics (provides heat, pressure, uplift); weathering and erosion (breaks down rocks); volcanism (creates new igneous rock). Time scales: millions to billions of years.