[EN] Mineral transformations of the gypsum-anhydrite system under microwave heating have been studied using in situ dielectric thermal analysis (MW-DETA) and Raman spectroscopy simultaneously. The dielectric properties of samples that were measured under microwave heating provided thorough information about the dynamics of the gypsum-anhydrite system transformations and its significance from the mineralogical point of view. In particular, the MW-DETA technique revealed a new intermediate phase with a gamma-anhydrite structure. This phase corresponds to the soluble stage of gamma-anhydrite, and it is characterized by a high ionic charge inside the crystal channels. The complete sequence is gypsum -> 0.625-subhydrate -> bassanite -> hydro gam...