Silica minerals are widely used in environmental remediation for their prevalence in soil and sediment. Two common SiO2 polymorphs, a-quartz and alpha-cristobalite, were investigated for the removal of a typical cationic dye, methylene blue (MB), from aqueous solutions. Their adsorption behaviors were studied in batch experiments as a function of specific surface area (SSA), pH, and temperature. The surface site density of a-quartz (10.6 sites/nm(2)) was higher than that of alpha-cristobalite (6.2 sites/nm(2)) with the Gran plot method, and the adsorption maxima of MB on the two were 0.84 mg/m(2) and 0.49 mg/m(2), respectively, at 303 K and pH 8. The potentiometric titration showed the capacity of proton-donating by alpha-quartz was stronger than that by a-cristobalite. A drastic increase of adsorption amount on alpha-quartz at pH < 3 was caused by its greater quantity of isolated silanols. The negative Delta G and positive Delta H values suggested adsorption of MB on both minerals was spontaneous and endothermic. At three different temperatures (288 K, 298 K, and 303 K), the adsorption capacities of two polymorphs increased with increasing temperature. The surface heterogeneity of alpha-quartz and alpha-cristobalite corresponds to their different adsorption behavior, and our work also provides some referential significance in evaluating the overall quality of soils and sediments. (C) 2015 Elsevier B.V. All rights reserved.