How does calcium sulfate form? Does it via a similar process than calcium carbonates i.e., crystallisation via a poorly-ordered precursor? Or does it occur via a different mechanism?
Because of the role of calcium sulphates in biomineralization (e.g., medusa statoliths) and its importance in industrial processes (e.g., plaster of Paris production) we are studying the early-stage structure and morphology of precipitated CaSO4. Results demonstrate that gypsum (CaSO4·2H2O) forms by an extremely rapid oriented self-assembly of bassanite (CaSO4·0.5H2O) precursors. Our first paper on this topic was published as a research article and front cover image in Science magazine.
I have also collaborated in a research project on sulfides by studying the crystallisation of mackinawite (FeS) and greigite (Fe3S4) from amorphous FeS. This study has relevant implications for the biogeochemical cycling of elements in anoxic and suboxic marine environments.
Van Driessche, A.E.S., Benning, L.G., Rodriguez-Blanco, J.D., Ossorio, M., Bots, P., García-Ruiz, J.M. (2012) The Role and Implications of Bassanite as a Stable Precursor Phase to Gypsum Precipitation. Science, 336, 69-72. doi: 10.1126/science.1215648 [PDF] [Supl. Info]
Stawski, T., Van Driessche, S., Ossorio, M., Rodriguez-Blanco, J.D., Besselink, R., Benning, L.G. (2016) Formation of calcium sulfate through the aggregation of sub-3 nanometre primary species. Nature Communications, 7:10177. doi:10.1038/ncomms11177 [PDF] [Supl. Info]
Csákberényi-Malasics, D., Rodriguez-Blanco, J.D., Kovács Kis, V., Rečnik, A., Benning, L.G., and Pósfai, M. (2012) Structural properties and transformations of precipitated FeS. Chemical Geology, 294-295, 249-258. doi: 10.1016/j.chemgeo.2011.12.009. [PDF]