Caliche

Caliche, also known as calcrete, duricrust, or hardpan, is a sedimentary rock, a cemented deposit of calcium carbonate and other minerals that binds other materials—such as gravel, sand, clay, and silt—together. It is generally found in arid or semi-arid regions.

Formation:

Caliche forms near the surface where evaporation exceeds precipitation. Water is drawn upwards through capillary action, dissolving minerals from the soil and bedrock. As the water evaporates at the surface or near-surface, the dissolved minerals, primarily calcium carbonate (CaCO3), precipitate out, cementing the surrounding soil particles together. Over time, repeated cycles of dissolution and precipitation lead to the formation of a hard, impermeable layer.

Composition:

While calcium carbonate is the dominant component, caliche can also contain other minerals like gypsum, silica, iron oxides, and clay minerals. The presence of these different minerals can influence its color, texture, and hardness.

Characteristics:

Caliche typically appears as a whitish or grayish layer in the soil profile. It can range in thickness from a few centimeters to several meters. Its hardness varies depending on the degree of cementation. In some cases, it is soft and easily broken, while in others it is extremely hard and rock-like. Caliche can also exhibit different morphologies, including laminar crusts, nodules, and massive beds.

Occurrence:

Caliche is commonly found in arid and semi-arid regions around the world, including the southwestern United States, Australia, southern Africa, and parts of South America. These regions typically experience high evaporation rates and have calcium-rich soils.

Uses and Impacts:

• Construction: Caliche can be used as a construction material, particularly for road base and building foundations. Its hardness and stability can provide a solid base for structures.
• Agriculture: Caliche can negatively impact agriculture by impeding root growth, reducing water infiltration, and affecting soil drainage. In some cases, it may be necessary to break up the caliche layer before cultivating the land.
• Paleoclimate studies: The composition and morphology of caliche can provide valuable information about past climate conditions, such as aridity and rainfall patterns. Stable isotope analysis of the calcium carbonate can also be used to reconstruct past temperatures.
• Geomorphology: Caliche plays a role in landscape evolution by influencing erosion rates and affecting the distribution of vegetation. It can protect underlying soils from erosion or, conversely, promote erosion by channeling water flow.