Importantly, this difference in the mesostructure is also observed for the re-precipitated gypsum crystals formed through the hydration of bassanite (Fig. , stage V). The question now arises, how can we rationalise the occurrence of these different mesostructures? It is known that the hydration of bassanite to gypsum involves a dissolution-reprecipitation process in contrast to solid-state diffusion , which is seemingly also the case for our gypsum-bassanite transformation. When we compare the two gypsum formation events (Fig. ), the first occurrence happens through mostly homogeneous nucleation upon mixing of the two stock solutions. However, all subsequent nucleation and crystallization events occur from heterogeneous solutions, as the growth of de novo crystalline phases occurs in the presence of dissolving preceding phase, and thus solid interfaces. This is the case for both bassanite and gypsum nucleation (Fig. , stages II-V). We propose that such heterogeneous surface-affected nucleation processes lead to the formation of less mesostructured crystals compared to those growing from homogeneous bulk solutions. Furthermore, as we discuss in the next section, the determined structural and morphological changes, as well as the structural disorder associated with phase transitions in brines, are driven by temperature-dependent changes in the solubility of bassanite and gypsum (Fig. ). These changes in solubility, in turn, control the rates of nucleation and crystal growth.