Morphological, Physico-Chemical and Clay Mineralogy Investigation on Gypsiferous Soils in Southern of Tehran, Iran

3 Abstract: In this study, based on topographic maps, satellite images and conducted several field visits, ten pedons studied in the area and for further study four representative pedons selected which occurring on two different landscapes (piedmont plain and hill). Occurrence of gypsum in studied soils related to weathering the parent material and climatic conditions. In all pedons were observed secondary gypsum in small crystalline with diameters of a few millimeters and in different forms. Gypsum content showed an increase with depth in middle of all pedons and then its content decrease in lower horizons. The XRD diffractograms indicate the presence of chlorite, smectite, illite, palygorskite and kaolinite as the major clay minerals in these soils. Chlorite, illite and kaolinite can be originated from parent material. The amount of smectite in the clay fraction increased with depth except in pedon 5 and as for smectite, palygorskite showed an increasing trend with depth in the pedons 2, 4. Probably inheritance and transformation from illite are the main ways for existence of smectite. Neoformation of palygorskite is believed to be the main mechanisms for the occurrence of this mineral in the studied soils.