Ejected rocks from the 1872 eruption of Vesuvius, Italy: a petrographic and mineralogical overview.

A set of 30 ejecta from the 1872 eruption of Vesuvius have been selected in the Scacchi's collection of the Real Mineralogical Museum of University Federico II (Naples) to study their petrographic and mineralogical features and to provide insight into their genetic processes. Petrographic study has established the occurrence of four varieties: 1) homogenous lavas (HL); 2) composite lavas (CL); 3) lavas and/or metamorphic rocks macroscopically conglomerate-like (LMC); 4) conglomerates (C). Mineral chemistry investigation has shown that the samples investigated consist of a large number of phases. These include minerals which typically occur in the Somma-Vesuvius lavas, like clinopyroxene, leucite (and other feldspathoids), plagioclase, K-feldspar and trioctahedral mica. Moreover a number of late to post-magmatic phases also occur. Textural, petrographic and mineral chemistry evidences indicate that phase crystallization are the result of a number of processes and complex interactions between rising lava, lava protholits and pulse of hydrothermal fluids and fumaroles at variable temperature and composition.