The minero-petrographic analysis of two flagstones ("basoli") recovered fron Treporti (Venice Lagoon) and Altinum

A sample of two stone blocks likely used as flagstones, one found in the course of underwater surveys at Treporti (Northern Venice Lagoon), and one still in situ in the vicinity of a Roman road at Altinum (now Quarto di Altino, province of Venice), the mother-town of Venice, were examined minero-petrographically by Powder X-Ray Diff raction and Polarised Optical Microscopy on thin section. The purpose of this study was to characterize the stones, compare them and possibly determine their original quarry. The results indicate that both blocks are composed by a lithic sandstone with very similar fabric and mineralogical composition, thus it may be concluded that they were very likely quarried in Roman times in the same geological formation. Both stones in fact correspond well to the so-called “molassa prealpina” a calcarenite/sandstone belonging to the Miocenic flysch formation outcropping in a wide north-eastern area of Italy running from the hills of Conegliano (province of Treviso) to those of Muggia (province of Trieste).