University of Kansas defines caliche as a broad term that defines sediment (sand, silt, gravel, and clay) or soil cemented together mostly with calcite in arid or semi-arid regions. Caliche may occur in small lumps (nodules) or may spread across miles.
Caliche is often found on or near the surface. Fresh caliche is soft and can be removed easily, but older deposits get hard and thick. Caliche is also known as calcrete, hardpan, and duricrust in some parts of the world. It is known as kankar in India.
Caliche is usually white, gray, brown, or reddish brown. Some fully developed and old specimens often look like breccia, coquina, sandstone, or conglomerate if the cemented particles in the rock are of the proper size and type.
Caliche’s strength depends on how well it is cemented. The resultant rock is extremely hard, dense, heavy, and durable if the cement fills the spaces between the soil or sediment particles. Specimens with poor cementing are weak and brittle.
Caliche is a common rock and is found worldwide. It is also an economically valuable rock because of its multi-dimensional use.
Caliche forms when calcium carbonate seeps from upper soil horizons by downward-percolating and runoff.
Calcium carbonate precipitates as small grains or thin coating on soil particles. The grain coating starts to thicken over time, and adjacent grains are cemented together. It forms nodules, and the cementing continues, resulting in a continuous subsurface layer.
The subsurface layer leads to a solid caliche layer in the advanced stage. The advanced layers can get dense and thick, stopping water seepage and erosion. Advanced caliche formation often produces layers thicker than 1 meter and extending up to 100 square kilometers.
Caliche usually forms in areas with rainfall less than 65 centimeters, and the mean annual temperature are above 5°C (41°F). Plant roots also play an important role in caliche formation because they release carbon dioxide into the soil.
Caliche can also form when the water rises upward through capillary action. The rainwater seeps quickly into dry regions. When the surface water dries out, the water below the surface rises and takes along the minerals in the soil. The minerals precipitate, and carbon dioxide evaporates.
Where is Caliche Found?
Caliche is a common rock and occurs worldwide. It is usually found in arid or semi-arid regions like deserts. The notable reserves are located in central and western Australia, the Kalahari desert in Southern Africa, High Plains in the USA, the Sonoran desert in Mexico, the Chihuahuan Desert in Mexico and USA, the Mojave desert in the USA, and Al-Ahsa in Saudia Arabia.
One of the world’s largest caliche reserves is located in the Makgadikgadi Pans in Botswana. It is also found in England, Texas, and Nevada.
Caliche is used in the construction industry to manufacture cement. However, it is a hard and durable material, and its processing is challenging. The walls of the Great House at Casa Grande Ruins National Monument, Arizona, US, were built with caliche. Mayans also used caliche to build mortars. People in South Australia used caliche to make homes during the 19th century.
Caliche is used in place of limestone to refine sugar. Although caliche doesn’t have the 95% calcium carbonate requirement to refine sugar, it works as an alternative because it is cheaper than transporting limestone.
Caliche development can also have valuable gemstones, minerals, and gold. Its porosity is a deposition site for valuable secondary minerals, uranium ores, and gem materials.
Despite its uses, caliche presents some problems as well. Fully developed layers don’t allow water to pass through the soil, so plant growth is impossible. Caliche is a barrier to erosion by wind or water. However, the erosion is rapid, channeled, and severe when it happens.