Built by a geologist
The Rock Cycle
Understanding how rocks form and transform is essential for any geologist. The rock cycle describes the continuous process of rock formation, breakdown, and reformation. Three Rock Types All rocks belong to one of three categories based on how they formed: 1. Igneous Rocks Formed from the cooling and solidification of molten material magma or lava : - Intrusive Plutonic : Cool slowly underground → large crystals granite, gabbro - Extrusive Volcanic : Cool quickly at surface → small crystals or glass basalt, obsidian 2. Sedimentary Rocks Formed from the accumulation and lithification of sediments or precipitation from solution: - Clastic : Made of rock fragments sandstone, shale, conglomerate - Chemical : Precipitated from solution limestone, rock salt, chert - Organic/Biogenic : From organic material coal, some limestone 3. Metamorphic Rocks Formed when existing rocks are changed by heat, pressure, or chemically active fluids: - Foliated : With layered/banded texture slate, schist, gneiss - Non-foliated : Without layers marble, quartzite, hornfels The Cycle in Action 1. Igneous rocks weather and erode 2. Sediments deposit and lithify into Sedimentary rocks 3. Burial and tectonic forces create Metamorphic rocks 4. Deep burial or subduction causes melting 5. Magma rises and cools to form new Igneous rocks The cycle has no beginning or end - rocks continuously transform from one type to another over geological time scales millions of years . Plate Tectonics Connection Different plate tectonic settings favor different rock types: - Mid-ocean ridges : Basalt extrusive igneous - Subduction zones : Andesite, metamorphic rocks - Continental interiors : Sedimentary sequences - Mountain belts : Metamorphic complexes