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 Sedimentary rocks are one of the three major kinds of rocks found in the crust of the Earth. Sedimentary rocks are formed by the accumulation and consolidation of layers of loose sediment or by the accumulation of chemicals that precipitate out of water. Sedimentary rocks cover 70% to 75%1 of the total area of the Earth's surface. However, they only make up 5% of the volume of the Earth's outer crust. Layers of sediment are deposited horizontally on the Earth's surface and naturally buried. This is where they are compacted and subjected to increased temperature and pressure, which eventually forms the sedimentary rock. The Grand Canyon is one of the most famous sites for viewing sedimentary rocks. This canyon exposes layers of limestones, shales, and sandstones.
There are two main categories of sedimentary rocks. Clastic rocks are those which form from mineral particles that are mechanically transported, including volcanic debris. The other major group of sedimentary rocks form as a result of the chemical precipitation of minerals, evaporation of mineral-containing waters, or the conversion of biological matter to rock.
Sedimentary rocks provide information about ancient environments. For example, a fine-grained shale rocks is made from mud formed in quiet waters, while carbonate rocks form from coral reefs or shallow marine environments.
Pictures: Above two pictures- Sedimentary Rock Feilds
1 The Grolier Multimedia Encyclopedia
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