Provenance of the ornamental stones used in the baroque church of S. Pietro in Valle (Fano, Central Italy) and commentary on their state of conservation

An archaeometric study of the ornamental stones in the interior of the baroque church of San Pietro in Valle (Fano) has been carried out. On the basis of mineralogical, petrographic and geochemical studies, the areas of quarrying of 44 lithotypes are firstly established and a complete database of the location of the decorative marbles in the church was also provided. Both marbles from the Mediterranean region, used in the Roman and Byzantine period, and stones more typically found in baroque buildings were widely employed. Among the ornamental stones of local (Italian) provenance, a large number of lithotypes from the neighbourhood of Verona (Veneto Region, northern Italy) has been found. It is worth noting that a fundamental role in choosing several marbles from Verona was played by Abbot Domenico Federici who arrived in Fano after he had been appointed secretary to the imperial embassy in Venice. Petrographic descriptions have been provided for Breccia di Brentonico, Lumachella di S.Vitale, Astracane di Verona and Nero Nube Conchigliato, which are four ornamental stones (never described in detail elsewhere) extensively quarried in the Venetian region. An isotope geochemistry study of the white marbles (Marmor Proconnesium and Marmor Lunense) has also been carried out. Most of the ornamental stones show severe and different forms of decay, and therefore, conservation work is strongly urged. Crystallisation of salts in the pores of the rocks is the main cause of the decay shown by most of the lithotypes. The soluble salts largely originate from (i) the rising damp, which affects the outer walls of the church, and subordinately from (ii) inappropriate works undertaken at the beginning of the 20th century when numerous marble slabs were re-attached with gypsum grouts. The high levels of relative humidity inside the church are not consistent with the most suitable conditions for the conservation of wall paintings and decorative stones.