Kalkification

Kalkification is the geological and geochemical process by which calcium carbonate (CaCO3) is deposited from dissolved ions in water to form solid calcium carbonate accumulations. In geology and geomorphology, it produces features such as travertine and tufa deposited from groundwater or surface springs, as well as speleothems like stalagmites and stalactites in caves. In soils and sedimentology, kalkification refers to the formation of calcium carbonate nodules and cementation of soil horizons, which can influence soil texture, drainage, and the mobility of nutrients.

The process is driven by chemical and physical conditions that promote calcium carbonate precipitation. Water becomes supersaturated with calcium and carbonate ions, often aided by the degassing of carbon dioxide as water rises or loses CO2 to the atmosphere, or by evaporation and cooling. Biological activity can also enhance precipitation, for example through photosynthesis in microbial mats or by organisms that create nucleation sites. Conversely, acidic inputs or changes in temperature, CO2 levels, or water chemistry can reduce precipitation or dissolve existing carbonate deposits.

Kalkification has practical and scientific significance. It affects water quality and infrastructure when calcium carbonate scales build up in pipes, boilers, and aquaria. It contributes to the stratigraphic record and paleoenvironments by preserving carbonate deposits that reveal past hydrological and climatic conditions. The term overlaps with calcification in biology and with diagenetic carbonate cementation in sedimentology, though in common usage kalkification emphasizes carbonate precipitation in natural waters and soils.