Abstract
Soils of Bangladesh have been formed from different kinds of parent materials and are spread over three major physiographic units: hills, terraces and floodplains. Clay mineral data were scarce till eighties, later, sporadically some works were done at both home and abroad. The available clay mineralogical data have been compiled and summarized for making a clay mineralogical map on the national basis. Mica was the predominant clay mineral in almost all the soils. Other major minerals were smectite (mainly iron-rich high-charge beidellite), chlorite, vermiculite, kaolinite, and interstratified mica-chlorite, mica-vermiculite-smectite and kaolinite-smectite, depending on the physiographic location of the soils. The proposed clay mineralogical map has eight mapping units: namely, Mc-Ch*, Mc-St, Mc-Vt*-Kt, Mc-Ch-Vt*, Mc-Mx-Kt, Kt-Mc, Mc-Kt-Vt* and Mc-Kt-Vt, where the symbols Mc, Ch, St, Vt, Kt, and Mx indicate mica, chlorite, smectite, vermiculite, kaolinite, and mixedlayer minerals, respectively, and asterisk (*) means partial chloritization of some vermiculite or partial degradation of some chlorite. This generalized clay mineralogical map well corresponded with the agroecological regions of Bangladesh.
