Soils that form in arid climates are predominantly mineral soils with
low organic content. The repeated accumulation of water in some soils
causes distinct salt layers to form. Calcium carbonate precipitated from
solution may cement sand and gravel into hard layers called “calcrete”
that form layers up to 50 meters thick.
Caliche is a reddish-brown to white layer found in many desert soils.
Caliche commonly occurs as nodules or as coatings on mineral grains
formed by the complicated interaction between water and carbon dioxide
released by plant roots or by decaying organic material.