The effect of chemical composition of diaspores on their electrokinetics was studied. Increasing SiO2 content in a diaspore sample was found to decrease its isoelectric point. The X-ray diffraction and SEM microanalysis showed the absence of distinct SiO2 phases. A linear correlation was found to exist between the measured isoelectric point and alumina to silica mass ratio in diaspore samples. The linear regression analysis of the experimental data suggests a more significant impact of silicon content than aluminum content, indicating a preferential adsorption of dissolved silicon on diaspore samples and/or preferential dissolution of aluminum from diaspore samples. (C) 2003 Elsevier Inc. All rights reserved.