Sodalite-group minerals from Somma-Vesuvius volcanic complex (Italy): a case study of K-feldspar-rich xenoliths

Sodalites and sulfatic sodalites in holocrystalline K-feldspar-rich ejecta from the Somma Vesuvius volcanic complex, Italy, have been characterized by combined chemical, structural and spectroscopic analyses. Sodalite has a relatively homogeneous chemical composition, with the ubiquitous presence of CO32- and H2O/OH-. The sulfatic sodalites are isomorphous and have cage structures which can contain a wide variety of anions, molecular species and cations. Molecular CO2 and H2O/OH- are present in sulfatic sodalites, instead of the CO32- anions that are present in sodalite sensu stricto. The cell dimensions of the all of the studied sodalite samples are very similar, the sulfatic sodalite cell dimensions are more variable. Structure refinement of a distinctly green sample confirms the P43n space group. Metasomatic magma-derived fluids that are rich in H2O, CO2, Cl and S are believed to be responsible for the genesis of the relatively late-stage phases which form the ejecta containing the sodalite-group minerals