Soil Mineralogy in the American Southwest.

Do desert soils, like those in the Southwest, have mineral suites different than other soils? In general, sand and silt mineralogy in desert soils more closely match their parent materials when compared to humid soils, although much silt is transported laterally by wind, thus mixing suites of silt minerals. Clay minerals in the form of small aggregates are also transported by wind across desert landscapes. However, a substantial amount of clay is formed in situ. Kaolinite, for example, is prominent in soils formed in granitic soils with high amounts of feldspar. Palygorskite and sepiolite with their fibers radiating into pore spaces are common in stage IV, V, and VI petrocalcic horizons. Other neoformed minerals include pedogenic carbonate, opal-A, opal-CT, various sulfates, and chlorides. In addition to their importance as a source of nutrients and their influence on water holding capacity, shrink-swell, and other physical properties, soil mineralogy carries a long-term “memory” of a soil’s environment in which it formed. Authigenic kaolinite, for example, is most likely a vestige from wetter glaciopluvial periods in the Pleistocene.