Sedimentary Rocks What are Sedimentary Rocks? • Sediment- fragments of rock that have been broken down as a result of weathering and erosion by wind, water, and ice. • Sedimentary Rock- formed by the accumulation and cementing/compacting of sediments. Types of Sedimentary Rocks • There are 2 types of sedimentary rocks: • Clastic sedimentary Rocks • Chemical Sedimentary Rocks Clastic Sedimentary Rocks • Clastic Rocks- Form from compacted sediments. • They are inorganic. • Classified by the size of the sediment. Conglomerate • Shale- smallest grains • Siltstone • Sandstone Shale • Breccia • Conglomerate- largest grains Chemical Sedimentary Rocks • Chemical Rocks- Made from the precipitation of water. • This is broken down into 2 categories: • Crystalline • Organic Crystalline Sedimentary Rocks • Crystalline Rocks- Form from a chemical process. • Also known as evaporites and precipitates. • Evaporite- sedimentary rocks formed by the evaporation of water. • Precipitate- forms when water is so full of a dissolved Dolostone mineral that the mineral no longer dissolves and crystallizes in the water. Rock Salt • Examples: • Rocks salt • Rock Gypsum • Dolostone Organic Sedimentary Rocks • Also known as bioclastic or biochemical sedimentary rocks. Coal • Organic Rocks- Made from compacted organic matter (things that were once living) • The only rock that contains fossils or evidence of life. • Depending on the grain size, an organic sedimentary rock can be chemical or clastic. Biochemical Limestone • Examples: • Coal • Biochemical Limestone Fossil • Fossils Sedimentary Rock Textures • How does the rock feel? • Clastic Sedimentary Rocks • You can see the grains with your eyes or with a magnifying glass. • If you rub the rock, dust particles are left on your hand. • Chemical Sedimentary Rocks • If it looks smooth like plastic or if you can see a crystal structure. Sedimentary Rock Composition • What is the rock made of? • Organic • If the rock contains a fossil, shells, or any other signs of former life, the rock is bioclastic/organic. • Inorganic • If the rock does not have any signs of life, then it only contains minerals. Classifying Sedimentary Rocks • Identify the rock’s: • Texture • Composition • Texture + Composition= rock name • Once the rock is identified, you can use it to learn about a region’s past. Why Study Sedimentary Rocks? • Sedimentary rocks are a great way to examine an area’s past. • The rock material and fossils present can help you make conclusions about how the environment used to be in a given area. • Example: • Based on evidence from sedimentary rocks, scientists were able to discover that Death Valley used to be a lake. Watch This and Fill Out Your Graphic Organizer https://www.youtube.com/watch?v=Etu9BWbuDlY.