Provenance of obsidians from the neolithic archaeological site of San Martino Spadafora (Messina - Italy) by Mössbauer spectroscopy

In the San Martino of Spadafora area (Messina-Italy), during the proceedings of the third line of the pipeline Eni-Snam, a Neolithic site was found, related to two diverse phases of occupation: Ancient Neolithic Age (of stentinelliana culture) and Late Neolithic (of Diana culture). Almost all lithic artifacts discovered in that site are made of obsidian (Neolithic black gold), a volcanic rock of dark color very rich of SiO2, used during the neolithic age to realize tools and objects. Due to the vicinity to the Aeolian Islands, the obsidians may came directly from Lipari; however, the chemical analysis point out slight differences in composition with respect to the Lipari outcrops. Therefore, a compositional comparison was performed, to see if the discovered obsidians have an extra territorial origin or if the differences are ascribable to lavic flows covered by successive eruptions. This allows to check whether San Martino site is part of a complex exchange network that encouraged the arrival of raw material from afar. The structural and compositional characteristics that made interesting to exchange high value obsidians, not only for their use but also for their symbolic and aesthetic value, may be highlighted, as well. We investigated the composition and provenance of different obsidian samples, S1 – S12, obtained from obsidian artifacts resulting from industry lithic chipped excavations. They were analyzed by transmission Mössbauer spectroscopy measurements performed at room temperature with a 57Co in Rh source; the spectrometer was calibrated using an α-Fe foil. The typical shape of the spectrum consists of an asymmetrical doublet. The presence of sextet subspectra, possibly ascribable to the presence of magnetite and/or hematite contributions [1,2], was not observed. The experimental spectra were simulated using three different quadrupole doublets (QD) as in obsidians the presence of two Fe2+ sites and one Fe3+ site is found [1,2,3]. Symmetrical quadrupole doublets were used, as a preferential texture is not expected [4]. The possible presence of QD distributions was considered, as well, but that did not improve the fitting quality, so each of the Fe ions chemical/structural environment seems to be rather uniformly reproduced within the sample. In this contribution, the results of the analysis performed on the obsidian samples will be presented and compared with the results obtained from obsidians coming from Aeolian islands and from other obsidian sites of the Mediterranean area. In particular, the Mössbauer data collected on S1- S12 display a negligible spread, indicating a common source for what concerns the artifacts from San Martino site. [1] A. Bustamante, M. Delgado, M. R. Lattini, A. V. Bellido, Hyperfine Interactions 175 (2007) 43. [2] M. Duttine, R. B. Scorzelli, G. Popeau, A. Bustamante, A. V. Bellido, M. R. Lattini, N. Guillaume Gentil, Hyperfine Interactions 175 (2007) 85. [3] R. B. Scorzelli et al., C. R. Acad. Sci. Paris 332 (2001) 769. [4] U. Gonser, Mössbauer Spectroscopy, Springer-Verlag (1975)