Most clay minerals are characterized by a platy morphology. By contrast, palygorskite has a fibrous morphology and is structurally distinct from the typical 1:1 and 2:1 layer structures. Diverse opinions exist on the origin of palygorskite in soils. Many authors suggest that palygorskite forms after smectite. Others favor its authigenesis during pedogenic processes or its inheritance from the parent material. This review provides a critical synthesis on the origin of palygorskite in the semi-arid-tropical (SAT) Vertisols and arid calcic soils of the Thar Desert of India. It also highlights the specific genetic pathway for the presence of palygorskite in the soils. The ubiquitous association of smectite with palygorskite is inadequate to explain the formation at the expense of smectite, because at pH 8.2 and above the smectite structure is subjected to dissolution to create soluble Si and Al, and the recrystallization of the soluble Si and Al to form palygorskite may not be possible in the Vertisols of the Indian SAT environment. Thus, mildly to moderate alkaline pedochemcial environments of the SAT Vertisols do not favor authigenic precipitation of the palygorskite in such soils. This review shows that the presence of palygorskite in the SAT Vertisols is due to its inheritance from the exhumed inter-trappean beds, infra-trappean beds, and bole beds. This view on the genesis of the palygorskite is also justified by its presence in weakly developed calcic soils of the Thar Desert as detrital flux from the adjoining marine sedimentary rocks.

Soils in similar geomorphic settings in hyperarid deserts (< 50 mm yr−1) should have similar characteristics because a negative moisture balance controls their development. However, Reg soils in the hyperarid southern Negev and Namib deserts are distinctly different. Soils developed on stable alluvial surfaces with only direct input of rainfall and dust depend heavily on rainfall characteristics. Annual rainfall amount can be similar (15–30 mm), but storm duration can drastically alter Reg soil properties in deserts. The cooler fall/winter and dry hot summers of the southern Negev Desert with a predominance brief (≤ 1 day) rainstorms result in gypsic-saline soils without any calcic soil horizon. Although the Namib Desert receives only 50–60% of the southern Negev annual rainfall, its rainstorm duration is commonly 2–4 days. This improves leaching of the top soil under even lower annual rainfall amount and results in weeks-long grass cover. The long-term cumulative effect of these rare rain-grass relationships produces a calcic-gypsic-saline soil. The development of these different kinds of desert soils highlights the importance of daily to seasonal rainfall characteristics in influencing soil-moisture regime in deserts, and has important implications for the use of key desert soil properties as proxies in paleoclimatology.