Hydration structure on dolomite: Telling calcium and magnesium apart

The hydration structure at the mineral-water interface is decisive for understanding fundamental reactions taking place at mineral surfaces, including mineral dissolution, growth and weathering. Recent advancements in three-dimensional atomic force microscopy (3D AFM) have opened the potential to directly image the hydration structure above a surface, providing unparalleled structural insights into mineralwater interfaces 1. Here, the hydration structures at the calcite-water 2 and dolomite-water 3 interface will be presented with an emphasis on discussing the differences that arise from the presence of magnesium in dolomite as compared to calcium in calcite. Analysing site-specific vertical positions of hydration layers and comparing them with molecular dynamics simulations unambiguously unravels the minute but decisive difference in ion hydration and provides a clear means for telling calcium and magnesium ions apart. 1 T. Fukuma, Y. Ueda, S. Yoshioka, H. Asakawa, Phys. Rev. Lett. 2010, 104, 016101 2 H. Sngen, M. Nalbach, H. Adam, A. Khnle, Rev. Sci. Instrum. 2016, 87, 063704 3 H. Sngen, C. Marutschke, P. Spijker, E. Holmgren, I. Hermes, R. Bechstein, S. Klassen, J. Tracey, A. S. Foster, A. Khnle, Langmuir 2017, 33, 125