This study deals with the identification of vermiculite in the presence of mica. Three natural silicates were first subjected to expansion by rapid heat treated at 400 degrees C. Then, the starting silicates and their derived heat-treated products were analyzed by X-ray diffraction, FT-IR spectroscopy, N-2 adsorption at - 196 degrees C, and helium density measurement. The adsorption of cadmium, chromium, and lead was also carried out. Two of the silicates are composed of mainly biotite and the other of biotite and vermiculite. In general, the results of X-ray diffraction, FT-IR spectroscopy, and helium density measurements are well in agreement. The heat treatment at 400 degrees C has little effect on the chemical composition, structure, and texture of the silicates. The development of microporosity is small in the silicates. Surprisingly, the adsorption capacity toward chromium and lead is larger for the biotite silicate than for the vermiculite containing silicate. (C) 2010 Elsevier B.V. All rights reserved.