Aluminosilicates represent the major group of solid inorganic matter of the terrestrial crust. In specific conditions of temperature and pressure, the aluminosilicates may, in strong alkaline environment, react among themselves, giving place to the formation of stable materials of high mechanical strength, able to support high levels of temperature and resistant to acid action. They also have the ability for the immobilisation of heavy metals and radionuclides. When subject to a previous thermal treatment, certain aluminosilicates like kaolin, can be directly activated at room temperature and normal pressure. In this work, the conditions of preparation of metakaolin (a meta-phase of kaolin) are optimised. Temperatures of kaolin dehydration and exposition time to temperature are studied by the use of XRD, FTIR and NMR-MAS, and so far by the application of Murat-Bachiorrini Criterion. The results obtained show that energy savings are considerable.