Chemogenic Deposit

a group of sedimentary rocks, minerals, and mineral products that form through the chemical precipitation of various substances from solution and their accumulation on the bottom of bodies of water.

The composition and conditions of formation of chemogenic deposits in humid climates differ considerably from those in arid climates. Chemogenic deposits may form in sea, continental, and intermediate basins. In humid climates such deposits are represented by iron and manganese ores, bauxites, phosphorites, and to some extent limestones and silica rocks. The constituent compounds are poorly soluble in water and therefore precipitate out of slightly mineralized water. In basins with higher salinity, which usually occur in the arid regions of the earth, various salts are precipitated. Where the salinity of seawater is weak (up to 15‰), dolomite, fluorite, celestite, gypsum, anhydrite, magnesite, and other minerals are precipitated. At a salinity of about 25‰, rock salt (halite) forms, and where salinity reaches 30–35‰ or higher, various potassium and potassium manganese salts of chloride and sulfate composition, such as sylvite, carnallite, bischofite, kainite, polyhalite, and langbeinite, occur. These minerals are associated with sulfates and carbonates. Concentrations of boron, lithium, rubidium, cesium, and other elements are associated with potassium and magnesium minerals.

While continental lakes that have no outlet to the sea become more saline, soda, sulfate, salt, and other chemogenic deposits accumulate. Soda, thermonatrite, and trona, accompanied by halite, thenardite, mirabilite, and other minerals, form in soda lakes. In addition, gypsum, thenardite, mirabilite, glauberite, astrakanite (bloedite), and other minerals form in continental salt lakes, which generally do not have potassium and potassium-manganese minerals. A heightened concentration of fluorine, strontium, bromine, and other elements is occasionally observed in the composition of saturated solutions (brine).

Chemogenic deposits, especially salt deposits, provide the raw material for the factory production of many chemical compounds and substances; they are also used in natural form for various purposes.