Ricerc@Sapienza

Natural Mg-rich lucchesiite was thermally treated in air and hydrogen atmosphere up to 800 °C to study potential changes in Fe-, Mg- and Al ordering over the octahedrally coordinated Y- and Z-sites, and to explore possible applications to intracrystalline geothermometry based on tourmaline. Overall, the experimental data (structural refinement, Mössbauer, infrared and optical absorption spectroscopy) show that thermal treatment of lucchesiite results in an increase of Fetotcontents at Z balanced by an increase of Mg and Al at Y.

An Fe-rich fluor-elbaite was thermally treated in air and hydrogen atmosphere up to 800 °C to study potential changes in Fe- and Al-ordering over the octahedrally coordinated Y and Z sites. Overall, the experimental data (structural refinement, electron and ion microprobe, Mössbauer, infrared and optical absorption spectroscopy) show that thermal treatment of fluor-elbaite results in an increase of Fe contents at the Z site balanced by an increase of Al at the Y site.

Twenty natural spinel single crystals displaying colors almost representative for the entire spinel variability were investigated by electron microprobe and UV–VIS–NIR–MIR and FTIR spectroscopies. Eight of them, selected among the Fe-bearing ones, were also analyzed by X-ray diffraction, and five by Mössbauer spectroscopy to obtain information on the oxidation state and site distribution of Fe.