The rock forms as primary deposits or through the replacement of existing rocks. In composition the deposits vary from a mixture of calcite and original material up to practically 100% pure calcite.Calcrete is a hardened deposit of calcium carbonate. This calcium carbonate cements together other materials, including gravel, sand, clay, and silt. It is found in aridisol and mollisol soil orders. Calcrete occurs worldwide, generally in arid or semi-arid regions, including in central and western Australia, in the Kalahari Desert, in the High Plains of the western USA, and in the Sonoran Desert.
Calcrete is also known as hardpan, caliche, kankar (in India), or duricrust. Calcrete is generally light coloured but can range from white to light pink to reddish-brown, depending on the impurities present. It is generally found on or near the surface, but it can be found in deeper subsoil deposits as well. The layers can vary from a few inches to feet thick, and multiple layers can exist in a single location.