Kaolinite and kaoliniferous sand were subjected to thermal or mechanical modification and subsequent acid activation to obtain amorphous materials. The physico-chemical, mineralogical and morphological properties were characterized. The results for the materials derived from the kaoliniferous sand were similar to those for washed kaolins, the difference was in the amount of kaolinite content in the samples. The mechanical treatment by eroding the initial structure altered the position of Al in such a way that it facilitated its extraction with acid preventing the formation of mullite at 990 degrees C. A strong increase is observed in the surface areas, the more pronounced effects are those found for the samples produced by mechanical modification followed by acid treatments (LOA-533 m(2) g(-1) and MOA-63 m(2) g(-1)) with micro- and mesopores being increased by this procedure, while samples produced by thermal modification followed by acid treatments (LTA-189 m(2) g(-1) and MTA-47 m(2) g(-1)) have only increased micropores. (C) 2009 Elsevier Ltd. All rights reserved.