Trioctahedral smectites and zeolites as transformation products of the Cala Pozzolana di Ponente pyroclastic rocks (Linosa Island - Italy)

On Linosa Island the pyroclastites of Cala Pozzolana di Ponente have been affected by post depositional alteration phenomena. Field and laboratory study point out that this pyroclastic deposit was affected by hydrothermal circulation with formation of secondary minerals like smectite, zeolites, calcite. The transformation processes were accomplished in two stages; a first one was brought about by the circulation of abundant hydrothermal fluids that reacted with the glass fragments producing a thin regular crust of smectite surrounding glass fragments and a second one, responsible for the zeolite growth, was accomplished by fluids enriched in alkalis and calcium released by the altered glass, in conditions of decreasing fluid circulation and falling temperature. -from Authors