Review What determines the size of the mineral grain in an igneous rock? Explain when magma will form a coarse-grained rock, a fine-grained rock, or glassy rock? What factors favor the growth of large crystals? What are extrusive rocks? Why are they easy to recognize as igneous? What are intrusive rocks? Hoe do geologists know they are igneous? Sedimentary Rock Sedimentary Rocks: (definition) • Formed by hardening and cementing of layers of sediments (rock fragments, organic remains, or chemicals that form on lake or ocean bottoms) • 75% of Earth’s surface covered with sediments & sedimentary rocks Sedimentary Rock 3 types: A) Clastic Sedimentary Rocks B) Chemical Sedimentary Rocks C) Organic Sedimentary Rocks A) Clastic Formed from fragments of other rocks. Formation: i) pre-existing rocks are weathered ii) the fragments are transported by wind, ice, and water (*the further the fragments travel, the more rounded they become) iii) the fragments are deposited according to energy and size = sorting Large fragments = high energy = rivers Medium fragments = med energy = beaches Small fragments = low energy = lakes, oceans A) Clastic Examples: • i) Shale – consists of tiny flakes of the mineral, little space. • ii) Sandstone – made up of grains of quartz, with space between particles. • iii) Conglomerate – cemented mixture of rounded pebbles and sand grains. i ii iii B) Chemical Formed from minerals dissolved in sea, lake swamp or underground. Ex. Great Salt Lake, Dead Sea Chemical sediments are formed when these minerals are precipitated from the water by evaportaion. Ex. Rock salt, Gypsum B) Chemical Great Salt Lake, Utah C) Organic Formed from remains of plants and animals Limestone from the skeletons of shell fish Coal from plants accumulating in shallow lakes or swamps Chert from the skeletons of silica radiolarians and sponges Sedimentary Features Stratification Fossils Ripple Marks and Mud Cracks Concretions and Geodes