For a comparison between the behaviour of pure metakaolinite and other clays or related minerals thermally activated at 750°C, the research has been extended to different calcined raw-materials, e.g. montmorillonite, illite, muscovite and phlogopite, impure natural clays, laterites and tropical soils, black colliery spoil and slate waste. The more reactive solids obtained by thermal activation are pure kaolinite and kaolinitic minerals such as tropical soils and laterites: the hydration of samples added with calcium hydroxyde and gauged at normal consistency leads to optimal 28 days strength from 15 to 27 MPa. Montmorillonite and illite lead to lower 28-day strength. Pure muscovite and phlogopite, black colliery spoil and slate waste do not present any interest in this field when thermally activated at 750°C. Some recommendations are given for a practical application of the research.