Pedogenic palygorskite is formed in oases soils in the eastern province of Alhasa. The pedogenesis of palygorskite is indicated by the fact that this clay mineral could not be detected in an ancient red bed (Miocene or Pliocene) believed to be the soil parent material. This pedogenic palygorskite is forming at the expense of the red-bed smectite, as the composition of the soil saturation extracts is found to fall within the stability field of palygorskite rather than smectite.