Sedimentary rocks are characterised by their formation from the deposition and lithification of rock material. They may be formed through physical and chemical processes, such as mechanical weathering, compaction and dissolving of rock material.
Sedimentary rocks may be formed through a process called lithification, which is the accumulation and compaction of sedimentary materials into solid rocks. Transportation through water systems such as rivers and oceans may cause clay, silt and other sedimentary materials to accumulate and form into rocks such as sandstone and shale. These rocks typically have smooth and rounded edges due to erosion from constant underwater motion.
Sedimentary rocks may be formed through the chemical dissolving and reforming of materials in rocks. Water sources that have a higher rate of evaporation than precipitation may facilitate the accumulation of sedimentary material, creating an environment in which the formation of new rocks becomes possible. Chemical weathering may cause materials such as calcium carbonate to accumulate and form new rocks such as limestone. Calcium carbonate is comprised of organic material, such as shells and coral, that have been broken down and dispersed in water sources and allowed to settle. The chemical properties of these rocks may be altered to form new rocks, such as dolomite, which is the result of limestone exposed to water containing magnesium.