Sedimentary rock is formed from the weathered remains of other rocks. Sedimentary rocks are formed from overburden pressure as particles of sediment are deposited out of air, ice, or water flows carrying the particles in suspension. As sediment deposition builds up, the overburden (or lithostatic) pressure squeezes the sediment into layered solids in a process known as lithification ("rock formation") and the original connate fluids are expelled.
Sedimentary rocks are composed largely of silica (i.e. quartz), with other common minerals including feldspars, amphiboles, clay minerals and sometimes more exotic igneous minerals. Sedimentary rocks are classified as clastic, that is, they are composed of discrete clasts of material (rather than being composed of organic material as is the case for a limestone).
Sedimentary rocks are economically important in that they can be used as construction material. In addition, sedimentary rocks often form porous and permeable reservoirs in sedimentary basins in which petroleum and other hydrocarbons can be found.
It is believed that the relatively low levels of carbon dioxide in the Earth's atmosphere, in comparison to that of Venus, is due to large amounts of carbon being trapped in limestone and dolomite sedimentary layers. The flux of carbon from eroded sediments to marine deposits is known as the carbon-cycle.
The shape of the particles in sedimentary rocks has an important effect on the ability of micro-organisms to colonize them. This interaction is studied in the science of geomicrobiology. One measure of the shape of these particles is the roundness factor, also known as the Krumbein number after the geologist W. C. Krumbein.