calcareous

Calcareous sandstone in Israel

Calcareous refers to a sediment, sedimentary rock, or soil type which is formed from or contains a high proportion of calcium carbonate in the form of calcite or aragonite.

It can also be used as an adjectival term applied to anatomical structures which are made of calcium carbonate in animals such as gastropods, when referring to such structures as the operculum, the clausilium, and the love dart.

Calcareous sediments are usually deposited in shallow water near land, since the carbonate is precipitated by marine organisms that need land-derived nutrients. The farther from land sediments fall, the less calcareous they are, usually. Some areas can have interbedded calcareous sediments due to storms or changes in ocean currents.

Calcareous soils are relatively alkaline soil. This is because of the very weak acidity of carbonic acid. Note that there are other causes for a high soil pH.

Calcareous coatings, or calcareous deposits, are mixtures of calcium carbonate and magnesium hydroxide that are deposited on cathodically protected surfaces because of the increased pH adjacent to the surface.

Calcareous ooze is a form of calcium carbonate derived from planktonic organisms that accumulates on the sea floor. This can only occur if the ocean is shallower than the CCD or carbonate compensation depth (CCD). Below this depth, calcium carbonate begins to dissolve in the ocean, and only non-calcareous sediments are stable, such as siliceous ooze or red clay.

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