Geochemical, mineral-petrographic and physical-mechanical characterization of stones and mortars from the Romanesque Saccargia Basilica (Sardinia, Italy) to define their origin and alteration

This paper aims to study the geomaterials of the most important Romanesque-style monument of Sardinia, the Santissima Trinità di Saccargia Basilica (Codrongianos, north Sardinia). The monument was built up on ruins of a pre-existing monastery, and completed in 1116 A.D. Over time, the aspect of the monument is quite changed due to two series of restoration works. The stone materials consist of both grey-black basalts and whitish limestones and marls, intentionally used to give a bichromy effect of the construction. The volcanic rocks belong to the Miocene-Pleistocene volcanic Sardinian activity, while limestones and marls belong to the sedimentary marine Miocene Formation of Meilogu (Logudoro). To define both the origin and the alteration processes of materials, geochemical, petrographic and physical-mechanical investigations of volcanic and sedimentary rocks were carried out on samples collected from monument and possible source outcrops. The integrated chemical (ICP-MS) and petrographic data allowed to ascertain the sourcing sites of raw materials. Moreover, physical-mechanical tests along with X-Ray Diffraction (XRPD) analysis, highlighted the main weathering processes responsible of the chemical physical alteration affecting the geomaterials, and the newly-formed mineral phases formed on stone surface.