Sedimentary rocks can roughly be classified according to how they form:
Clastic sedimentary rocks are formed by the buildup of numerous pieces of other rocks, which are cemented together by compaction, or the infiltration of some other mineral. They are usually classified by particle size:
Some are of mixed particle size, classified by particle shape:
Organically-formed sedimentary rocks are essentially accumulated organic matter: Material excreted by organisms, or left behind after their death.
Chemically-formed sedimentary rocks are the result of chemical processes in the deep ocean, or in soils: