This study focused on understanding the influence of different amounts of calcite impurities (0 to 10% by mass) on the optimal parameters for clay dehydroxylation and the reactivity of the final calcined clay. A surface response experimental design was used to study the effect of maximum temperature, residence time and calcite content on different experimental responses. Specific surface and particle size distribution were used to characterize the physical properties of the calcined-clays. SEM coupled with EDS was selected to study the particle morphology and the composition of the amorphous phase formed, while XRD was used to assess the mineralogical composition after calcination. TGA analysis was used to measure the remaining amounts of kaolinite and calcite after calcination, while isothermal calorimetry was used to assess the reactivity of the different calcined-clays obtained. It was observed that specific surface area is the most sensitive parameter to variations in calcite content.