Sedimentary rocks are derived from sediments by diagenesis (increase in pressure and temperature by landfill). Sediments are deposited in sedimentary basins (and thus in sea water), except for some lake sediments (non-saline lakes) or frankly land sediments (boulders, glacial sediments as loess ...). A sediment is an accumulation of biological, chemical, and mineral elements. The sediment is a living environment, it still contains a large amount of water. During diagenesis, the water is expelled and life is scarce. · The elements of biological origin (skeletons, shells, tests, fragments of plants ....) and precipitation of chemical elements by living organisms (limestone and silica mainly) seem to be present in all sedimentary rocks. · The minerals from the degradation of other rocks (detrital components) by erosion and mainly accumulated in the basin as a result of transport by rivers can be in a greater or lesser amount. Minerals of volcanic origin (or pyroclastic volcano-sedimentary) as ash can also form very thick sedimentary layers or mix with particles from other sources. · The elements due to pure chemical precipitation sometimes form large accumulations exploited by man (named evaporite rock mines) as from the evaporation of sea water, such as sea salt: sodium chloride ( $NaCl$ or halite) and gypsum ( $CaSO_4\cdot2H_2O$ ). A sedimentary rock is often a mixture of elements of different sizes and from different sources, so that the classifications are very varied.
- Origin: calcareous sand, shelly sand - Minerals: calcite or aragonite ( $CaCO_3$),
- Origin: calcareous sand - Minerals: dolomite ($(Ca, Mg)CO_3$ ) by partially replacing $Ca$ in calcite
- Origin: calcareous sand with a lot of clay - Minerals: clays ($ Si, Al, Fe, Mg SiO_x $) and calcite (CaCO_3 $ $)
- Origin: silica sand - Minerals: quartz (SiO_2 $ $)
- Origin: very deep deposit of radiolarian siliceous mud - Minerals: quartz, chalcedony, opal ($ SiO_2 $)
- Origin: sludge diatoms (small unicellular algae) - Minerals: quartz, chalcedony, opal ($ SiO_2 $)
- Origin: pebbles (puddingstone) or angular blocks (breccia) caught in a thinner cement, sandy or clay - Minerals: various