Abstract. This paper focuses on the authigenic mineralization processes
acting on “Tufo Rosso a Scorie Nere” (TRS), i.e. one of the main pyroclastic units of the Vico
stratovolcano (Latium, Italy). The pyroclastic deposits appear in general
massive and made of “black vitreous vesiculated juvenile scoriae”,
immersed in an ashy matrix lithified after zeolitization processes. The main
minerals are chabazite and phillipsite, and the zeolitic content is locally
variable, reaching 68 % wt. Zeolites grow replacing both amorphous
fraction and pre-existing phases, occurring inside both matrix and scoriae.
Concerning scoriae, zeolitization moves from the rim to the core of the
scoriaceous fragment as a function of (a) temperature of the fluids and (b)
permeability (primary or secondary). Composition of parental fresh glass and
that of zeolitized rocks is compatible with trachyte chemistry, lightly
undersaturated in SiO2, and the alteration processes modified the
parental rock chemical features. Zeolites genesis is ascribed to a
“geoautoclave-like system”, and zeolites display a Si/Al ratio similar to
that of the parental glasses. TRS presents promising mineralogical
characteristics as supplementary cementitious material in the production of
mixed cements.