caliches

Caliches, or caliche deposits, are hardened accumulations of calcium carbonate (CaCO3) that form in the soils of arid and semi-arid regions. They represent a duricrust, a hard horizon within the soil profile, and appear as crusts, nodules, or layered bands that can range from a few centimeters to several meters in thickness.

Caliche forms when groundwater rich in calcium and bicarbonate moves through the soil and evaporation concentrates the dissolved minerals near the surface. Leaching removes more soluble components from upper horizons, leaving calcium carbonate to precipitate and bind soil particles. Over time, calcite cementation hardens the horizon, producing a dense, durable layer.

Caliche occurs in several forms. Nodular caliche consists of discrete carbonate nodules embedded in the soil; crustose caliche forms a continuous, brittle crust at or near the surface; layered caliche develops successive carbonate-rich horizons. In some regions caliche is part of a broader duricrust that can include other minerals, such as gypsum or silica, producing duripans or carbonate-gypsum crusts.

Caliches are widespread in deserts and semi-arid areas, including the southwestern United States, northern Mexico, parts of South America, Africa, the Middle East, Australia, and parts of Asia. They influence soil properties by reducing permeability and restricting root growth, complicating agriculture and construction, and affecting groundwater recharge. In some locales caliche is mined for lime and used as building material.

The term caliche derives from the Spanish caliche, meaning lime or limestone, and the plural caliches refers to multiple deposits or nodules.