Is amorphous calcium sulfate a common precursor phase to bassanite and gypsum?

Calcium sulfate minerals (i.e. gypsum, anhydrite and bassanite) are ubiquitous on Earth and they are highly relevant chemical compounds for a wide variety of industrial processes. The current consensus based on state-of-the-art synchrotron and electron microscopy data, is that the formation of crystalline phases in the CaSO4-H2O system is non-classical involving several steps, including an intermediate amorphous
phase. The overarching issue that remains to be resolved is whether all three phases of CaSO4, and in particular gypsum and bassanite,
follow the same non-classical pathway entailing a common precursor amorphous phase? With this proposal we aim to use SAXS/WAXS to
follow in situ and in a time-resolved manner the evolution of species forming from aqueous solutions containing calcium and sulfate ions. We propose an experiment in which bassanite or gypsum are formed selectively under directly comparable, thermodynamic conditionsdiffering only slightly in temperature.