The kinetics of garnet formation by solid state reactions is investigated by pre‐sintering and sintering the mixture of Fe2O3, Y2O3, and Al2O3 at several temperatures. The Mössbauer effect study of reaction products allows a quantitative determination of incorporated Al ions in the garnet structure. A separation of the phases containing iron such as hematite, orthoferrite, and garnet are carried out from Mossbauer spectra collected at 300 °C. The magnetization measurements and Curie temperatures support the results of Mössbauer effect study.