Calcreous

Calcreous, also spelled calcareous, is an adjective used in geology, paleontology, soil science, and biology to describe substances or formations that are composed of calcium carbonate or contain significant amounts of calcium carbonate minerals such as calcite or aragonite. The term derives from the Latin calcareus, meaning limestone-like, from calx, lime.

In geology and sedimentology, calcreous materials are common in the fossil record and in modern sediments. Calcreous sediments are formed from the accumulation of calcium carbonate from organisms such as corals, foraminifera, and mollusks, and can lithify into limestone, chalk, or other carbonate rocks. Calcareous ooze, a deep-sea sediment consisting largely of microfossil remains, is a prominent example.

In biology, calcreous describes shells, skeletons, and tests of organisms that are made primarily of calcium carbonate. Examples include mollusk shells, coral skeletons, and the tests of certain algae and foraminifers. Calcareous hard parts contribute to biogenic carbonate deposits and influence paleoceanographic reconstructions.

In soils and landscapes, calcreous soils are those containing a substantial fraction of calcium carbonate, often raising soil pH and causing effervescence with dilute acid. These soils influence plant communities and nutrient availability and can form duric horizons in arid regions, such as calcretes or caliche.