The phase composition of coal combustion ashes is important in regard to their potential uses. Here it is shown that a combination of phase separation techniques with X-ray diffraction, thermogravimetric analysis, and conventional chemical analysis, including elemental analysis and wet chemistry, can be used to obtain a fairly complete phase composition. The application of these techniques is illustrated with an FBC ash sample, indicating the procedures used to achieve the identification of calcium silicates, aluminates and ferrites, and their quantitative estimates. A new method for the quantitative determination of CaO in presence of large amounts of Ca(OH)(2) has been developed which uses phase separation as a previous step to chemical titration.