High-C fly ashes from the Peage de Roussillon power plant in France are characterized and used to synthesize SiAlONs by carboreduction. A nearly pure beta-phase can be obtained by heating the raw materials without any special preparation, such as carbon addition or grinding, at 1500 degrees C for 1 hour, The high-C fly ashes are thus valuable and very economic starting products for preparing SiAlONs.