This paper presents the results of a study of the linear hydric dilatation of some sandstones and meta-sandstones and its relations with their mineralogy, texture and physical properties. The ultimate aim is to identify the main factors and mechanisms responsible for hydric dilatation in silicoclastic rocks. The study has been conducted on various rock types selected for their different mineralogical, textural and physical properties: Macigno, Monte Senario and Manciano sandstones, and Pietra del Cardoso and Monte Pisano Quartzite meta-sandstones. In the selected samples, linear hydric dilatation measured perpendicular to rock bedding or foliation ranges from 0.15 to 1.01 mm/m. The results herein obtained indicate that the main factors influencing the degree and kinetics of dilatation upon water uptake are the amount, size and size distribution of the open pores, the pore shape and spatial distribution, the preferential orientation of phyllosilicates and the presence of significant amounts of expansible clayey components. These factors combine and interact in various ways to generate the different hydric behaviours observable in these stones. In particular, the linear hydric dilatation depends at first on the pore dimensions in respect to the absolute water absorption.

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