Fine clay, coarse clay, and silt fractions of four Bangladesh soils were studied using XRD, ion exchange, and selective dissolution techniques. Constants for the XRD intensity-weight proportion relationships were derived using these techniques. Smectite and mica were found to be dominant in Batra and Ghior soils, whereas kaolinite and mica were dominant in the Naraibag and Ghatail soils. Other minerals present were vermiculite, vermiculite with hydroxyaluminium interlayers, chlorite, randomly interstratified chlorite-mica, feldspar, quartz, and trace amounts of amphibole. The amorphous material content varied between 1 and 11% and decreased with increasing particle size. No crystalline iron oxides were detected in untreated clay fractions.