Mesoporous materials were obtained from two natural silica sources, diatomite and pumicite, under hydrothermal conditions, autogenic pressure and in presence of the surfactant cetyltrimethylammonium bromide (CTAB) as the template. Using diatomite, a temperature of 383 K and the following molar ratios in the initial reaction gel: SiO2/Al2O3 = 8.86; CTAB/SiO2 = 0.1; Na2O/SiO2 = 0.10-0.25 and H2O/Na2O = 250-300, the mesoporous material MCM-41 was obtained in a reaction time of 48h. When pumicite was used, a mesoporous material was obtained in a reaction time of 96 h, a reaction temperature of 423 K and an initial reaction gel with the following molar ratios: SiO2/Al2O3 = 8.86; CTAB/SiO2 = 0.1; Na2O/SiO2 = 0.25 and H2O/Na2O = 330. (c) 2006 Society of Chemical Industry.