Sodalite-group minerals from the 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 CO 3 2– and H 2 O/OH – . The sulfatic sodalites are isomorphous and have cage structures which can contain a wide variety of anions, molecular species and cations. Molecular CO 2 and H 2 O/OH – are present in sulfatic sodalites, instead of the CO 3 2– 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 P 3 n space group. Metasomatic magma-derived fluids that are rich in H 2 O, CO 2 , 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.