Chemical Composition and Charge Behaviour of Smectites in Vertisols of Rajasthan

Chemical composition and charge behaviour of smectites were studied in seven soil series of Vertisols in Rajasthan, using structural formulae. Among these series Patan, Aklera, Chambal and Kota were derived from basalt, whereas Taswaria, Taswaria sodic and Bhatewar originated from calcic gneiss complex. Smectites from Vertisols of basalt were rich in total and free iron oxide whereas their counterparts from gneiss complex were higher in oxides of alkali and alkaline earth metal oxides. However, drainage and alluviation induced the variability in total as well as free iron oxides in the former. The source of charge was tetrahedral and octahedral in smectites of Patan, Aklera, Chambal and Kota, whereas tetrahedral was only the source of charge in Taswaria, Taswaria sodic and Bhatewar. Charge relationship revealed that smectites were intermediate in composition between montmorillonite and nontronite in the former while beidellite and nontronite in the latter.