Section 4-4 How do sedimentary rocks form? What are sediments? What is the difference between compaction and cementation? How are sedimentary rocks classified?

Sedimentary rocks are formed when sediments become pressed or cemented together or when sediments precipitate out of a solution. Sediments are the loose materials such as rock fragments, mineral grains, and bits of plant and animal remains that have been moved by wind, water, ice, or gravity.

Sedimentary rocks form as layers because of deposition Sedimentary rocks form as layers because of deposition. Older rocks are found at the bottom and newer rocks are found on top. Compaction – the process of layers of small sediments becoming compressed by the weight of the layers above them If the sediments are larger like pebbles, pressure alone will not cause them to stick together. Cementation – the process in which large sediments are glued together by minerals deposited between the sediments

Classification of Sedimentary Rocks Detrital – are made from the broken fragments of other rocks and are compacted and cemented together; are also called clastic rocks because of their texture (clastic means broken) Chemical – form when minerals are precipitated from a solution or are left behind when a solution evaporates Organic – form from the remains of once living things

Detrital Chemical Organic