The solubility limit of Al in hematite and of Fe/III/ in corundum was determined by X-ray diffraction and by Mössbauer methods using synthetic samples. Calibration curves were plotted for the determination of Al, resp. Fe in these minerals by both methods. Mössbauer spectroscopy was used for the determination of the distribution of Fe 2O 3 between hematite and hydrogarnet phases in red muds.