caliche

1. 1. A crude sodium nitrate occurring naturally in Chile, Peru, and the southwest United States, used as fertilizer.
   2. See sodium nitrate.
2. See hardpan (sense 1).

[American Spanish, from Spanish, pebble in a brick, flake of lime, from cal, lime, from Latin calx, calc-, lime. See calx.]

A soil that is mineralogically an impure limestone. Such soils are also known as duricrust, kunkar, nari, kafkalla, Omdurman lime, croute, and race. Many soil profiles in semiarid climates (that is, those characterized by a rainfall of 4–20 in. or 10–50 cm per year) contain concentrations of calcium carbonate (CaCO₃). This calcium carbonate is not an original feature of the soils but has been added during soil formation either by direct precipitation in soil pores or by replacement of preexisting material. Fossil analogs of caliche, which are widely reported in ancient sedimentary sequences, are referred to as calcrete or cornstone. See also Limestone; Soil.

The principal control on the formation of caliche is a hydrologic regime in which there is sufficient moisture to introduce calcium carbonate in solution to the soil but not enough to leach it through the system. As a result, calcium carbonate precipitates in the soil during periods of evaporation, and it will slowly increase in amount as long as the hydrologic setting remains stable. The source of the carbonate may be from the dissolution of adjacent limestones, from the hydrolysis of plagioclase and other silicates, or from carbonate loess.

Within the climatic constraints noted above, most caliche forms in river floodplains and near the surface of alluvial fans. In addition, caliche deposits may form within exposed marine and lacustrine limestones during periods of sea-level fall or lake desiccation. Caliche may also form at inert pediment (eroded rock) surfaces; in the geological record such surfaces will be seen as unconformities. In this context it is interesting that the first unconformity ever recognized as such, by James Hutton in 1787 on the Isle of Arran, western Scotland, is characterized by a development of caliche. See also Unconformity.

The mineralogy of the host soil or rock in which a caliche develops may vary considerably; it is not essential for there to be any preexisting carbonate grains within the regolith. The most favorable medium is a clay-rich soil of limited permeability. Low permeability provides the residence time in the soil pores necessary for calcite to precipitate. See also Calcite; Regolith.

A chernozem soil of the American south-west containing thick carbonate deposits.

Gravel, sand, or desert debris cemented by porous calcium carbonate or other salts.

A hard deposit of white limestone that sometimes underlies alkaline soils in and climates.

Calcareous deposit in arid areas from leaching and desiccation on rock surfaces and forming earthy crusts.

Caliche may refer to:

• Caliche (mineral), a hardened deposit of calcium carbonate.
• Caliche slang, a collection of slang words unique to Salvadoran Spanish.

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