Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being . The term is used in a wide variety of Science disciplines.
In zoology
Calcareous is used as an adjectival term applied to anatomical structures which are made primarily of calcium carbonate, in animals such as
, i.e.,
, specifically in relation to such structures as the operculum, the
clausilium, and the
love dart. The term also applies to the calcium carbonate tests of, often, more-or-less microscopic
Foraminifera. Not all tests are calcareous;
diatoms and
radiolaria have
siliceous tests.
The are calcareous organisms, as are the Calcarea (Calcarea), that have spicules which are made of calcium carbonate.Richard C. Murphy (2025). 087850138X, The Darwin Press, Inc.. 087850138X
Additionally, reef-building corals, or Scleractinia, are calcareous organisms that form their rigid skeletal structure through the precipitation of aragonite ( i.e., a polymorph of calcium carbonate).
In botany
Calcareous grassland is a form of
grassland characteristic of soils containing much calcium carbonate from underlying chalk or
limestone rock.
In medicine
The term is used in pathology, for example in
calcareous conjunctivitis, and when referring to
calcareous metastasis or
calcareous deposits, which may both be removed surgically.
In geology
The term
calcareous can be applied 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.
Marine sediments
Limestone are typically deposited in shallow water closer to land, as marine organisms that precipitate calcium carbonate primarily reside within shallow water ecosystems due to an inability to precipitate calcium carbonate at depth (see carbonate compensation depth). Generally speaking, the farther from land sediments fall, the less calcareous they are, and deviations from this expectation arise if (a) the ocean floor is shallower than the CCD or (b) storms/ocean currents transport calcareous sediments away from their origin point, leading to the
interbedding of calcareous sediments in alternative locations.
An additional form of calcareous marine sediment consists of calcareous ooze, which is a form of calcium carbonate sediment that consists of >30% biogenous material predominantly consisting of organisms such as and foraminifera.
Calcareous soils
Calcareous soils are relatively
alkaline, in other words they have a high pH. They are characterized by the presence of calcium carbonate in the parent material; the
Carbonate ion is a base. Additionally, these soils may have a calcic horizon, a layer of secondary accumulation of carbonates (usually calciumcarbonate or magnesiumcarbonate) in excess of 15% calcium carbonate equivalent and at least 5% more carbonate than an underlying layer.
List of calcareous rivers
Man made deposits
Calcareous deposits can form in water pipes.
An example of this is
Sunday stone.
In electrochemistry
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.
