Chemical Sedimentary Rocks

The chemical sedimentary rocks are different from that of sedimentary rocks. Process of formation/creation of chemical sedimentary rocks differentiates them from the sedimentary rocks. Elements with a mineral crystal structure that gets dissolved and saturated in water leads to the formation of these rocks. The water that contains dissolved minerals, upon evaporation result into the formation of chemical sedimentary rocks. Unlike other types of rocks, the chemical sedimentary are not classified on the basis of particle size. The mineral component of these rocks is taken into account for the purpose of classification. After understanding what chemical sedimentary rocks are, let us now get into the details of different types of rocks and related facts.

Types of Chemical Sedimentary Rocks

There are different types of chemical sedimentary rocks and their classification is carried out on the basis of minerals contained. The process of chemical sedimentary rock formation also plays an important role in their classification.

Carbonate Rocks
Formation of the carbonate rocks takes place by means of biochemical processes. Organisms like snails, corals and clams do the job of extracting carbonate minerals from water. Minerals are used by these creatures for making their exoskeletons. The exoskeletons, after the death of these animals fuse together to form rocks. Minerals like calcite and dolomite are the main constituents of carbonate rocks. Zooplankton and algae are responsible for the formation of calcite. Limestone is an example of carbonate rock which contains calcite to a higher degree.

Coquina is a type of limestone formed of shell fragments. Limestone, which is formed from exoskeletons of algae is known as chalk. There is another form of chalk called micrite. The texture of chalk is a bit more gritty than micrite. Oolithic limestone is a type of limestone. It is formed of spheres called ooliths. These spheres have a size equal to that of sand-grains.

Dolostone is a rock just like limestone which contains carbonate compounds. Dolomite is the main constituent of dolostone. This rock is actually the altered form of limestone. Properties of dolostone and limestone, in most cases are the same. In few cases, the texture gets destroyed due to recrystallization.

Chert
It is one of the forms of a mineral called quartz. Properties of chert are same as that of quartz; however, their structure is different. The chert rock, just like carbonates is created by biochemical processes. Diatoms are a type of algae which produce the chert rock through biochemical processes. The mineral called silica is extracted from water by these algae and exoskeleton. Death of diatoms results into the formation of a siliceous layer. This layer is then converted into chert rock by means of lithification. Radiolarian is another organism which plays an important role in the formation of chert rocks.

Evaporite Rocks
Halite and gypsum are the important examples of chemical sedimentary rocks. Formation of these rocks takes place as a result of saturation of water with salts. Total Dissolved Salts (TDS) is the unit for measuring how saturated a particular solution/water is. Normal seawater is saturated up to 34,000 ppm (parts per million) of salts. The TDS value for precipitation of gypsum is 100,000. Salinity level of water has to reach 350,000 ppm for the precipitation of halite. These precipitated salts further become compact and turn into rocks.

The chemical sedimentary rocks have different uses; some of the rocks contain minerals that are essential for your health; one of the examples of such mineral is epsomite; this mineral is used for soaking the feet. Halite is used as a salt in the preparation of food. Use of limestone as fascia in the construction of buildings is well-known. The chemical sedimentary rocks are therefore, important minerals which have many applications in day-to-day life.