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Sedimentary Rock Classification Dana Desonie, Ph.D. Say Thanks to the Authors Click http://www.ck12.org/saythanks (No sign in required) To access a customizable version of this book, as well as other interactive content, visit www.ck12.org CK-12 Foundation is a non-profit organization with a mission to reduce the cost of textbook materials for the K-12 market both in the U.S. and worldwide. Using an open-content, web-based collaborative model termed the FlexBook®, CK-12 intends to pioneer the generation and distribution of high-quality educational content that will serve both as core text as well as provide an adaptive environment for learning, powered through the FlexBook Platform®. Copyright © 2014 CK-12 Foundation, www.ck12.org The names “CK-12” and “CK12” and associated logos and the terms “FlexBook®” and “FlexBook Platform®” (collectively “CK-12 Marks”) are trademarks and service marks of CK-12 Foundation and are protected by federal, state, and international laws. Any form of reproduction of this book in any format or medium, in whole or in sections must include the referral attribution link http://www.ck12.org/saythanks (placed in a visible location) in addition to the following terms. Except as otherwise noted, all CK-12 Content (including CK-12 Curriculum Material) is made available to Users in accordance with the Creative Commons Attribution-Non-Commercial 3.0 Unported (CC BY-NC 3.0) License (http://creativecommons.org/ licenses/by-nc/3.0/), as amended and updated by Creative Commons from time to time (the “CC License”), which is incorporated herein by this reference. Complete terms can be found at http://www.ck12.org/terms. Printed: December 14, 2014 AUTHOR Dana Desonie, Ph.D. www.ck12.org C HAPTER Chapter 1. Sedimentary Rock Classification 1 Sedimentary Rock Classification • Describe how sedimentary rocks are classified. • List some common sedimentary rocks. Can you tell which type of rock these are? If you look up close, you would be able to see grains of sand. From this distance, you can see different layers from where the sand was laid down. This rock is sandstone. The sand grains are cemented together to make sandstone. Sandstone is a common type of sedimentary rock. Types of Sedimentary Rocks The main types of sedimentary rocks are clastic or chemical. Some sedimentary rocks are a third type, organic. Clastic sedimentary rocks are made of sediments. The sediments differ in size. Chemical sedimentary rocks are made of minerals that precipitate from saline water. Organic sedimentary rocks are made from the bodies of organisms. Clastic Sedimentary Rocks Clastic sedimentary rocks are grouped by the size of the sediment they contain. Conglomerate and breccia are made of individual stones that have been cemented together. In conglomerate, the stones are rounded. In breccia, the stones are angular. Sandstone is made of sand-sized particles. Siltstone is made of smaller particles. Silt is smaller than sand but larger than clay. Shale has the smallest grain size. Shale is made mostly of clay-sized particles and hardened mud. TABLE 1.1: Sedimentary Rock Sizes and Features Rock Conglomerate Breccia Sandstone Siltstone Shale Sediment Size Large Large Sand-sized Silt-sized, smaller than sand Clay-sized, smallest Other Features Rounded Angular 1 www.ck12.org When sediments settle out of calmer water, they form horizontal layers. One layer is deposited first, and another layer is deposited on top of it. So each layer is younger than the layer beneath it. When the sediments harden, the layers are preserved. Chemical Sedimentary Rocks Sedimentary rocks formed by the crystallization of chemical precipitates are called chemical sedimentary rocks. Dissolved ions in fluids precipitate out of the fluid and settle out, just like the halite pictured below ( Figure 1.1). FIGURE 1.1 The evaporite, halite, on a cobble from the Dead Sea, Israel. Living creatures can help chemicals become sedimentary rocks. Limestone is an example. Organic Sedimentary Rocks The bodies of organisms can make a sedimentary rock. Plant bodies are lithified to become coal. When shells are cemented together they make a type of limestone. So limestone can be considered chemical or organic. Some Common Sedimentary Rocks Listed below are some common types of sedimentary rocks ( Table 1.2). TABLE 1.2: Common Sedimentary Rocks Picture 2 Rock Name Conglomerate Type of Sedimentary Rock Clastic (fragments of non-organic sediments) Breccia Clastic www.ck12.org Chapter 1. Sedimentary Rock Classification TABLE 1.2: (continued) Picture Rock Name Sandstone Type of Sedimentary Rock Clastic Siltstone Clastic Shale Clastic Rock salt Chemical precipitate Rock gypsum Chemical precipitate Dolostone Chemical precipitate 3 www.ck12.org TABLE 1.2: (continued) Picture Rock Name Limestone Type of Sedimentary Rock Bioclastic (sediments from organic materials, or plant or animal remains) Coal Organic Vocabulary • chemical sedimentary rocks: Rocks that form from the hardening of chemical precipitates. • clastic sedimentary rocks: Rocks that form from hardening of sediments by compaction and/or cementation. Summary • Sediments settle out of water in horizontal layers. • Clastic sedimentary rocks are classified based on how they form and on the size of the sediments. • Chemical sedimentary rocks precipitate from fluids. Explore More Use the resource below to answer the questions that follow. • Sedimentary Rocks at http://www.youtube.com/watch?v=Ox_3z_lW-Hw (7:13) MEDIA Click image to the left or use the URL below. URL: http://www.ck12.org/flx/render/embeddedobject/1608 1. 2. 3. 4. 5. 6. 7. 4 List the three types of sedimentary rocks. Where and how are clastic rocks found? How do clastic rocks form? Contrast conglomerates and breccia rocks. What can be found in clastic rocks? Explain the difference between layers and bands. What can we learn from sedimentary rocks? www.ck12.org Chapter 1. Sedimentary Rock Classification 8. How do chemical rocks form? 9. What are bioclastic rocks? 10. List the two types of biocalstic rocks. Review 1. Describe the three main types of sedimentary rocks. 2. How can different types of limestone be bioclastic, chemical and organic? 3. List sedimentary rock types by grain size, from small to large. References 1. Mark A. Wilson (Department of Geology, The College of Wooster). Halite forming on a rock in the Dead Sea. Public Domain 5