Sodalite-group minerals from the Somma-Vesuvius volcano (Naples, Italy): a combined EPMA, SIMS, and FTIR crystal-chemical study.

This work is focused on the crystal-chemical characterization of the cationic and anionic components of sodalite-group minerals (SGM) occurring in various igneous-to-metamorphic rocks and ejecta from the alkaline-potassic Somma-Vesuvius volcano (southern Italy). A combination of different analytical techniques, i.e., XRD, SEM, EPMA, SIMS, FTIR, and mu-FTIR-FPA imaging, were used. Minor and trace volatile elements (H, C, and F) have been quantified for the first time (to the authors' knowledge) by SIMS, and in situ ion probe data were integrated with information derived from FTIR spectroscopy. The studied samples correspond to sodalite sensu stricto, nosean, and hauyne. SIMS measurements for H, F, and C (quantified as H2O, F, and CO2 wt.%, respectively) show contents 0.02-5.0 wt.% H2O, 0.01-0.14 wt.% F, and 0.08-2.95 wt.% CO2. Within the single crystals, the F and, to a lesser extent, CO2 concentrations are homogeneous, whereas, in terms of H2O, they range from relatively homogenous to strongly zoned. Single-crystal FTIR spectra of SGM can be grouped into sodalites and noseans/hauynes, according to the occurrence of the (CO2)-C-12 absorption at 2340 cm(-1). The absorption due to H2O or OH groups occurs as a very broad band extending from 3700 to 3000 cm(-1). FTIR data show the presence of CO32- in all samples. The collected data allow us to fully characterize the SGM from Somma-Vesuvius, and also provide some constraints regarding their genesis. These data can contribute to a more detailed understanding of the crystal chemistry of SGM, their geological environments of formation, and possibly of the technological characteristics of their synthetic analogues.