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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 © 2012 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/NonCommercial/Share Alike 3.0 Unported (CC BY-NC-SA) License (http://creativecommons.org/licenses/by-nc-sa/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: February 28, 2013 AUTHOR Dana Desonie, Ph.D. www.ck12.org C ONCEPT Concept 1. Sedimentary Rock Classification 1 Sedimentary Rock Classification • Describe how sedimentary rocks are classified. 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. Clastic sedimentary rocks are made of sediments. The sediments differ in size. Chemical sedimentary rocks are made of minerals that precipitate from saline water. 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 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. 1 www.ck12.org 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. 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) www.ck12.org Concept 1. Sedimentary Rock Classification TABLE 1.2: (continued) Picture Rock Name Breccia Type of Sedimentary Rock Clastic Sandstone Clastic Siltstone Clastic Shale Clastic Rock Salt Chemical precipitate Rock Gypsum Chemical precipitate 3 www.ck12.org TABLE 1.2: (continued) Picture Rock Name Dolostone Type of Sedimentary Rock Chemical precipitate Limestone 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. Practice 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 for more content. 4 www.ck12.org 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Concept 1. Sedimentary Rock Classification List the three types of sedimentary rocks. List the characteristics of clastic rocks. 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? How do chemical rocks form? What are bioclastic rocks? List the two types of biocalstic rocks. Review 1. Describe the two main types of sedimentary rocks. 2. Compare and contrast chemical sedimentary rocks and clastic sedimentary rocks. 3. List sedimentary rock types by grain size, from small to large. 5