Application of non-destructive XRF method to the study of the provenance for archaeological obsidians from Italian, Central European and South American sites

This paper presents the results of the attribution of approximately 1700 artifacts, from Italian, Central European and South American sites to the geological obsidian sources. The provenance was determined using the non-destructive X-ray Fluorescence (XRF) analytical method, based on the secondary X-ray intensity proposed by Crisci et al. (1994) and optimized by De Francesco et al. (2008). In the first phase of the research, to test the non-destructive XRF method, the analysis on entire obsidian fragments (similar to archaeological waste) was initially carried out on 60 samples representative of all the geological outcrops in the Mediterranean region. The secondary X-ray intensities obtained by non-destructive XRF on whole pieces were compared with the results using the XRF method on powders, carried out on the same samples (major elements, and selected trace elements, such as Nb, Y, Zr, Rb and Sr) as exhaustively described in De Francesco et al. (2008). These five trace elements were sufficient to characterize (by both methods) the different places of obsidian origin, because they are particularly indicative of the genetic processes that produced obsidian. The provenance of the obsidian artifacts was determined by comparing the X-rays intensity ratios of the selected elements with those obtained on the entire fragments of the obsidian sources in the Mediterranean. The purpose of this paper is to show the results obtained in almost two decades of the application of the non-destructive XRF method. About 1700 archaeological obsidian fragments, from numerous Italian, Corsican, central European (Romanian) and South American (Central-western Argentina and Central Chile) archaeological sites, have been analyzed by non-destructive XRF, and assigned to obsidian sources. The provenance of 97% of the obsidian artifacts was successfully determined. The results demonstrate that the non-destructive XRF method - thanks to its sensitivity, low cost, and high speed - is an extremely valuable tool for the attribution of the provenance of archaeological obsidian in the areas under consideration.