“…[ 4 ] Gypsum thermal transformations have been repeatedly investigated using various methods (see, for example, the literature [ 5–14 ] ). The first endothermic peak on the DTA curves associated with gypsum degradation is observed at 393–413 K [ 29,30 ] or at 413 K. [ 7 ] It should be noted that according to Raman spectroscopic (RS) data, it is fixed at 388 K [ 10,31 ] or at 360–425 K [ 8 ] and at 382–413 K according to SR‐PXD. [ 1 ] The initial temperature of the effect, as a rule, is about 373 K [ 10 ] and varies depending on the content of impurities of alkali halides in gypsum, the thermal history of sample, the size, shape and compactness of the starting gypsum (crystal or powder), as well as experimental conditions, in particular, heating rate, calcination time, and air exchange.…”