Mineralogy and charge of Moroccan vertisoil smectite

In this study,the clayey fractions from vertisols of five major agricultural regions of morocco,the chaouia,the gharb,the zaërs,the doukkala and the saïs were studied. a reference smetite,the wyoming montmorillonite (swy-1) was used for comparison. x-ray diffraction on samples subjected to mg and k saturations,as well as solvations using ethylene glycol and heating to 550°c allowed the identification and the semi quantification of the mineral species constituting the clay fraction. the interlayer charge of the 2:1 clays was estimated by the method of intercalation by the alkylammonium chains. cec was also determined before and after saturation with lithium and heating to determine total cec and tetrahedral cec. the results showed that the clayey fractions of the five moroccan vertisols studied are essentially constituted of smectites associated to variable,but often weak amounts of illite,kaolinite,chlorite,quartz and feldspars. the smectites of the vertisols of the chaouia and the zaër are beidellitic,while those of the gharb,saïs and doukkalas are mixed beidellite and montmorillonite. the alkylammonium method revealed that the interlayer charge of the smectites varied between 0.57 mol(c) for the vertisol of the chaouia and 0.36 mole(c) for that of the doukkala. the total,octahedral and tetrahedral cecs were in agreement with the charge determined by the alkylammoniums. the clayey fractions studied presented high total cec,variying from 85,3 and 108,5 cmole+/kg and varying tetrahedral cec ranging from 45,8 and 76,4 mole(c)/kg,reflecting the nature of the smectites (beidellite vs. mixed beidellite-montmorionnite) in clay mineralogy of each soil.