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SEDIMENTARY ROCKS FORMATION… • All sedimentary rocks form from the compaction and cementation of sediments • Sediments are small pieces of rocks and shells that have been transported and deposited by water, wind, gravity or ice (glaciers) IMPORTANT PROCESSES…. •Weathering: breakdown of rocks at the Earth’s surface •Erosion: transportation of sediments to new locations •Deposition: sediments are laid down/dropped in a layer IMPORTANT PROCESSES…. • Compaction: happens when sediments are deeply buried; weight and pressure of overlying sediments squeezes out air & water and presses sediments tightly together • Cementation: takes place when dissolved minerals are deposited in the tiny spaces among the sediments; acting like glue or cement to turn loose sediment into solid rock • Common cementing minerals: calcite, silica, iron oxides, clay minerals • The combination of theses two processes together is called lithification CLASSIFICATION OF SEDIMENTARY ROCKS…. • Sedimentary rocks are divided into two categories: • 1) Clastic: composed of weathered bits of rocks, minerals, or shells • Classified by particle size • Includes shale (most abundant), sandstone, conglomerate CLASSIFICATION OF SEDIMENTARY ROCKS…. • Sedimentary rocks are divided into two categories: • 2) Non-Clastic • A. Chemical: form when dissolved substances precipitate, or separate from water (through evaporation or precipitation) • Includes chert, flint, agate, halite, gypsum • B. Organic: Formed from dead plant material, shells, and skeletal material made by living things that have been buried and compressed. • Includes limestone, coal HOW TO KNOW…. • How to know if your looking at sedimentary rock… • In addition to noticing larger pieces of rock or shell, seeing the textures such as • Ripple marks indicate water once flowed • Mud cracks form when saturated mud dries out. • Fossils from the remains of plant and animals **these would all be destroyed by the processes that form igneous and metamorphic rock.