MINERALOGY OF DESERT SOILS IN THE HADRAMAWT VALLEY (YEMEN) AND CHANGES FOLLOWING IRRIGATION

The mineralogy of calcareous salinized Desert soils in the Wadi Hadram awt valley (Yemen) was studied. The soils were located in different pa rts of the valley (adjacent to the channel, at intermediate sites, and on a piedmont terrace), differed in their degree of salinity, and had been under irrigation for different lengths of time. The finely dispe rsed separates of the Desert soils and sediments consisted mainly of p alygorskite, which accounted for more than 50 percent of the total con stituents of this fraction, and much smaller amounts of hydromica of t he sericite-muscovite type (15-24 percent), magnesium-iron chlorites ( 4-9 percent), kaolinite (6-9 percent), sepiolite, mixed-layer formatio ns of two types (totaling no more than 2 percent), and finely disperse d quartz. During pedogenesis, the structure of all components of the c lay fraction was degraded and sericites were transformed into rectorit e. Human intervention led to changes in the behavior of minerals of th e carbonate group, layered silicates, and most of all, the mixed-layer formations.