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 is also used to refer to relatively alkaline soil. Frequently this is indeed due to a high calcareous content but 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.

Sedimentary rocks | Soil chemistry