In this experiment six different soil series, which were representative soils of Mashhad plain, were studied. These series included Bahrabad,Rëzvan,Kenebist , Ghiasabad,Borzeshabad and shirshotor.X—ray technique was used to determine the minerals present in the clay fraction of the soils. In general,mica,Montmorillonite, Kaolinite and chlorite were the dominant species in these soils.In a few samples, considerable amount of attapulgite ias also observed.Mica,Kaolin and chlorite are the most evenly distributed in all of the samples.In Bahrabad,Kenebist and Ghiasabad,Montmorilonite shows an abnormal behavior with glycerol treatment.This seems to be due to the presence of a low charge montmorillonite in the samples. Presence of attapulgite in series of Rezvan,Borzeshabad and Shirshotor may be related to high amount of gypsum and lime. This alkalin condition is a major factot in attapulgite formation.
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