The sulfate-bearing associations of fumarolic environments of Somma-Vesuvius volcano (Italy): a review from historical samples (Royal Mineralogical Museum of Naples)

The sulfate-bearing sublimate samples from Somma-Vesuvius, collected in the Royal Mineralogical Museum of Naples University Federico II (Italy), record historical exhalative events of this volcano, whose products are no longer available in outcrops. The complex associations have been thoroughly investigated using various analytical methods, including SEM-EDS, PXRD, SC-XRD, FTIR, and Raman spectroscopy. Sulfates (Cu-, alkali-Cu-, and Pb-bearing sulfates) are the most widespread group, closely followed by halides and then oxides, phosphates, and arsenates, often occurring as rare mineral associations. Among sulfates, kaliochalcite, KCu2(SO4)2[(OH)(H2O)], is the most abundant phase, followed by chalcanthite Cu(SO4)·5H2O. In some cases, both chalcocyanite, CuSO4, and chalcanthite are found in the same sample, indicating incomplete alteration of the anhydrous phase. Cyanochroite, K2Cu(SO4)2·6H2O, is also common, in association with other alkali-Cu sulfates, Pb sulfates, and atacamite, Cu2(OH)3Cl, in sky-blue encrustations. Steklite, KAl(SO4)2, fedotovite, K2Cu3(SO4)3O, and eleomelanite, (K2Pb)Cu4O2(SO4)4, are recorded for the first time at the Vesuvius volcano, while eleomelanite represents the second reported worldwide occurrence besides the type locality. Unusual phases containing As, Cd, and/or Tl (i.e., Tl-bearing leucite), as well as N, have also been identified. The presence of both HT and LT sublimates and alteration minerals indicates a progressive cooling of fumaroles, or the variation of genetic conditions at small scales. The presented FTIR and Raman data can be especially relevant in consideration of the potential occurrence of sulfates in planetary bodies.