The scattering data contain a plethora of information regarding phase, morphology and size evolution during the transformation reactions because we measured a continuous, gapless signal for 0.1 nm -1 < q < 35 nm -1 . Based on this data, we elucidated the structural changes taking place during the conversion reaction. One important aspect is that as the calcium sulfate crystals evolve, they exhibit orientation-dependent anisotropic 2D intensity profiles (c.f. Fig. ). This phenomenon is a characteristic feature of the calcium sulfate system when characterized using a flow-through capillary . Specifically, both gypsum and bassanite primarily form acicular single crystals . As the crystals reach sizes of a few hundreds nanometers to several micrometers, they align themselves with the flow along their long-axes as they pass through a horizontally mounted capillary. This leads to a texture in an otherwise polycrystalline system (SI: Fig. , SI: Fig. ). Additionally, at small-angles and at length-scales >>1 nm, a texture is also observable because calcium sulfate single crystals are internally mesostructured , meaning that they consist of slightly misaligned crystallographic domains, resembling brick-in-the-wall-like units. The direction-dependent intensity variations were clearly observable for the diffraction rings (wide-angle scattering, WAXS), as well as for the scattering around the beamstop in the center (small-angle scattering, SAXS) (SI: Fig. , SI: Fig. ). The extent of the anisotropy evolved with time following the temperature profile and is related to the changes in crystal phase, size, and morphology (SI: Fig. ). Therefore, the analysis of orientation-dependent changes in intensity and the crystal morphology of calcium sulfate provides valuable insights into the crystallisation mechanisms, which will be discussed in the following paragraphs. In Fig. we present the evolution of peak areas from the reflections at q bass ~10.42 nm -1 , characteristic of bassanite (110), and q gyp ~8.25 nm -1 , characteristic of gypsum (020), as shown in Fig. . The trend, as a function of T and time, reveals changes in anisotropy as the crystalline phases evolve.