sedimentary rock (thing) by Gorgonzola

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:
- Sandstone
- Greensand (aka Marl)
- Mudstone
- Siltstone
- Shale
- Arkose
Some are of mixed particle size, classified by particle shape:
- Conglomerate
- Breccia
Organically-formed sedimentary rocks are essentially accumulated organic matter: Material excreted by organisms, or left behind after their death.
- Coal
- (Some) Limestone e.g.
  - Stromatolites
  - Chalk
  - Coral
Chemically-formed sedimentary rocks are the result of chemical processes in the deep ocean, or in soils:
- Chert (with variations like Agate, Chalcedony, and Flint)
- Limestone including varieties such as
  - Dolomite
  - Oolite
- Duricrusts such as Laterite (aka ironstone) and Bauxite