Sedimentary rocks are types of rock that are formed by the deposition and subsequent cementation of that material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles (detritus) to settle in place.
Sedimentary rocks are classified by the way that they are formed. There are three different sub-categories of sedimentary rocks: clastic, chemical and organic. Clastic sedimentary rocks are rocks that are formed from bits and pieces of previously existing rock that are compacted or cemented together. They are differentiated by the size of the particles, or clasts, found within them, for example, sandstone is made of sand sized particles. Chemical sedimentary rocks are rocks that were formed from the minerals left behind when bodies of water evaporate. Gypsum and rock salt are examples of chemical sedimentary rocks. Organic sedimentary rocks are made from the preserved remains of organisms. Bituminous coal and organic limestone are examples of organic sedimentary rocks.
Select Sedimentary Rocks to learn more about the classification and identification of sedimentary rocks.