Carlo Lugliè

Neolithic Obsidian Economy Around the Monte Arci Source (Sardinia, Italy): The Importance of Integrated Provenance/Technology Analyses

With few exceptions linked to locally available options, obsidian is almost the unique lithic resource used for the production of chipped stone industries in the Neolithic sites of central-southern Sardinia. However the local economy of this raw material, an important clue to support hypotheses on the dynamics of interregional interactions, had in the past been largely neglected. In order to fill this gap we initiated (Luglie et al. 2007) a programme of “integrated” studies of Sardinian Neolithic obsidians involving the exhaustive study of reduction techniques, obsidian tools use and provenance of selected Early and Middle Neolithic assemblages. We also reached a better level of knowledge of the field occurences and geochemical variations of the Monte Arci obsidians. The archaeological obsidian sourcing was realized by a non-destructive association of visual and geochemical characterizations. We discuss here the present status of this approach from the Sardinian Early Neolithic (EN) sites of Su Carroppu (Luglie et al. 2007), Rio Saboccu (Luglie et al. 2008) and Sa Punta cases.

Geochemical characterisation of pozzolanic obsidian glasses used in the ancient mortars of Nora Roman theatre (Sardinia, Italy): provenance of raw materials and historical–archaeological implications

The study focused on the volcanic glass used in the production of bedding mortars and concrete of the Roman theatre (I cent. AD) of the Nora site. The volcanic glasses were frequently used as aggregate and with pozzolanic function in all hydraulic mortars of the different sectors of the building (e.g., concretes of tribunalia vaults and external niches, jointing and foundation mortars of cavea tier ashlars, brick bedding), together with mainly quartz-feldspar sands, local Oligo-Miocenic andesitic-dacitic volcanics and Palaeozoic and Tyrrhenian sedimentary rocks. These volcanic glasses show characteristics closer to obsidian than to natural pozzolan normally used in the Roman period. They have definitely not sourced locally, unlike the other components that make up the aggregate. To identify their provenance, a petrochemical comparison between several samples taken from the theatre mortars and the volcanic outcrops of some probable Sardinian source areas is made. The use of the not local pozzolanic glass is a technical innovation in the mortars of the Nora archaeological site, and considering the wide use of obsidians in the prehistoric periods for the production of tools, significant considerations about its origin, procurement and use are made.