Stone quarries during the Roman age: petrographical and petrophysical features of granitoid rocks exploited in Calabria (Southern Italy)

In this work, we carried out a petrographical and petrophysical investigation on granitoidrocks exploited in Calabria (southern Italy) during the Roman age.As it is known, granitoid rocks were employed as worthy building materials during theRoman times; starting from I century A.D., Romans exploited these lithotypes all over theMediterranean area and brought them in the main centres of the Empire where they weremainly used for manufacturing slabs and pillars. According to the literature (Galetti et al.,1992), the main extraction sites were in Egypt (Aswan and Eastern Desert), central Italy(Giglio, Elba e Sardinia islands) and north western Turkey. Solano (1985) reports aboutanother quarry in Calabria (southern Italy) dating to the first century A.D. on the basis ofpottery and coin findings. He also proposed that the quarry was possibly abandoned in A.D.369 after an earthquake destroyed the town of Nicotera, where the extraction site was located.Cirrincione et al. (2004) and Antonelli et al. (2010) comprehensively investigated thepetrography and geochemistry of Granito di Nicotera, as it was termed. Nevertheless,Cirrincione et al. (2003) and Solano (2003) reported the occurrence of another ancientextraction site located about 15 km north of Nicotera, close to the town of Parghelia, whichwas declared in 2011 “Important archaeological site of Italy” by the Italian Ministry ofCultural Heritage and Activities. As testified by numerous surveys, the quarry permits directobservations on Roman exploitation technology and provides new information about thegranite trade in antiquity. The present study focuses on the granitoids exploited in the twoRoman quarries, which differ in terms of petrographic and geochemical features. This is alsoreflected in different petrophysical properties and rock quality. Indeed, the “Granito diNicotera” is mostly a homogranular weakly peraluminous tonalite characterized by isotropicfabric, whereas the typical rock type at the quarry of Parghelia is a strongly peraluminousporphyritic granodiorite. Moreover, at the site of Parghelia two varieties have beendistinguished: one consisting of porphyritic granitoids with K-feldspar megacrysts (up to10cm in lenght), commonly defining a magmatic foliation and set in a medium- to coarsegrainedmatrix. On the contrary, in the other detected group K-feldspar megacrysts are rarerand reach only 3-4 cm in length; matrix forming minerals are the same as in the first group(Cirrincione et al., 2013). The average compressional wave velocity value is 4.7km/s for“Granito di Nicotera”, with rock Quality Index (QI; Tourenq et al., 1971) ~ 80%. Theporphyritic variety of Granito di Parghelia is characterised by visible microfracturing mostlydeveloped around feldspar megacrysts, and shows relatively low velocity values (average ~4.0 km/s) inhomogeneously distributed even at the handscale. This causes a physical behaviour, in agreement with textural features, to be heterogeneous even within the samelithotype and an overall poor elastic quality. QI ranges from 50% (at the microfractures) to ~80% (average matrix). Compared to the porphyritic group, the heterogranular one showshigher velocity and QI values (average ~ 4.9 km/s and 83%, respectively). The features ofgranitoids cropping out at the quarry could explain the reason because, after the quarry ofParghelia was dismissed it was not reactivated anymore, differently from the “Granito diNicotera” extraction site, which has been instead exploited until recent times.