To establish the critical salt concentration for a rapid gypsum to bassanite transformation (assuming, arbitrarily, <1 h to be a practical threshold), a series of experiments at different salt concentrations were carried out at T = 90 °C using unstirred batch reactors. These experiments revealed that a NaCl concentration of >4 M is needed to induce rapid (<1 h) transformation times (SI: Table ). At lower salt concentrations, such as 1.4 M NaCl, the transformation rate is significantly reduced, with gypsum not transforming to bassanite even after 11 days. Additionally, the critical temperature for a rapid gypsum-to-bassanite transformation was established at 4.8 M NaCl. Table in SI, shows that only at T = 90 °C, the transformation is fast (<1 h) in unstirred reactors. Experiments conducted at T = 70 °C indicate that it takes up to 5 days to transform gypsum to bassanite, which from an industrial perspective is not interesting. But it does confirm again that in high salinity solutions, the solubility crossover is shifted to much lower temperatures than those predicted by the thermodynamic calculations.