Scanning electron microscopy and energy dispersive spectrometric microanalysis of crystalline deposits following evaporation of CO$_3$H$^-$, Mg$^{2+}$ and Ca$^{2+}$ containing aqueous solutions

This paper is the first application of scanning electron microscopy (SEM) and of energy dispersive selection micro- analysis (EDS) to the study of natural spa waters used as sprays in current dermatological practice; the aim was to relate the mineral composition of the spray to the sensitory perception recorded by the patients. Crystallized deposits were first obtaine d on a collodion film, from two spa waters mainly containing hydrogenocarbonate, calcium and magnesium ions, but differing by their Mg/Ca ratio. In order to understand the types of crystals formed, mineral solutions of simpler composition were prepared and submitted to the same process. Among the crystalline varieties of calcium carbonate, calcite and vaterite were characterized ; aragonite could not be detected in spa waters deposits, despite the presence of magnesium, which favours the crystallization of this orthorhombic form in the artificial solutions.