calcareous

Calcareous is a descriptive term used for materials or substances that are composed mainly of calcium carbonate (CaCO3) or contain significant amounts of lime. The term derives from Latin calcareus meaning lime-bearing, from calx, calc- “lime, stone.” In geology, biology, and soils, calcareous materials are those rich in calcium carbonate or lime.

Common calcareous rocks include limestone, chalk, and travertine, which form by deposition of carbonate minerals from water or by metamorphism of carbonate rocks. The shells and skeletons of many organisms—corals, mollusks, foraminifera, coccolithophores—are calcareous, contributing to sediment when organisms die. Calcite and aragonite are two crystalline forms of CaCO3 that may be present.

Calcareous sediments, or calcareous ooze, accumulate on the seafloor where carbonate-secreting organisms excrete CaCO3. These deposits are dominant in many shallow warm seas, but their preservation is limited in deeper waters where CaCO3 dissolves. Over geological time, calcareous rocks may undergo diagenesis, dissolution, or metamorphism.

In soils, calcareous describes soils with high carbonate content, usually alkaline, often with a calcic horizon or caliche (duricrust) that forms in arid or semi-arid environments. Such soils tend to be poor in soluble nutrients and can affect plant growth and irrigation.

Calcareous materials are used commercially as building stones (limestone, marble), lime and cement production, and in many industrial processes. The distinction between calcareous and non-calcareous depends on calcium carbonate content, not on origin.