Cordierite has been synthesized by heating mixtures of kyanite and talc, using kyanite powders of two different sizes. The reaction is studied by thermogravimetric and differential thermal analysis. Phase changes are followed by X-Ray diffraction of samples fired between 750 °C and 1400 °C. The evolution of the reaction starts with the dehydration of talc at approximately 880 °C. The kyanite decomposes at approximately 1140 °C. The first traces of α-cordierite appear at around 1200 °C. The influence of the kyanite particle size on the kinetics and microstructure is analyzed.