Calcification

Calcification is the formation or deposition of calcium carbonate in biological structures. It produces structures such as shells, coral skeletons, and some microscopic plankton coverings.

Biomineralization: The process by which living organisms produce minerals or mineralized structures. Calcification is one form of biological mineral production.
Coral: A marine invertebrate animal that often forms colonies and secretes a calcium carbonate skeleton. Corals use calcification to build the framework of coral reefs.
Ocean acidification: The long-term decrease in ocean pH, driven mainly by seawater absorption of atmospheric carbon dioxide. It reduces carbonate-ion availability and can make calcification more difficult.
Calcification (pathology): The abnormal deposition of calcium salts in soft tissues, often involving calcium phosphate rather than calcium carbonate. The same word commonly names a medical process that differs chemically from biological carbonate formation.
Calcium carbonate: A chemical compound, CaCO₃, found in minerals such as calcite and aragonite. This is the mineral deposited in the biological structures defined as calcified.
Mollusk shell: A hard protective covering secreted by a mollusk, commonly composed largely of calcium carbonate. Shell growth is a familiar example of calcium carbonate deposition by an animal.
Ocean deoxygenation: The decline in dissolved oxygen in ocean waters caused by warming, nutrient pollution, and other processes. Low oxygen can co-occur with acidification and stress calcifying marine organisms.
Silicification: The deposition of silica in or around biological structures or geological materials. It is another form of mineralized structure, but uses silicon dioxide rather than calcium carbonate.
Calcite: A crystalline form of calcium carbonate with a trigonal crystal structure. Some organisms build calcified structures from this calcium carbonate polymorph.
Coccolithophore: A single-celled marine alga that often covers itself with calcium carbonate plates called coccoliths. Its microscopic plates are produced by biological calcification.

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