NON-DESTRUCTIVE ANALYTICAL METHOD BY XRF FOR DETERMINATION OF PROVENANCE OF ARCHAEOLOGICAL OBSIDIANS FROM THE MEDITERRANEAN AREA. A COMPARISON WITH TRADITIONAL XRF METHOD

A non-destructive analytical method using wavelength-dispersive X-ray fluorescence(WDXRF) that allows the establishment of the provenance of archaeological obsidians wasdeveloped and a comparison with the classical XRF method on powders is discussed.Representative obsidian samples of all the geological outcrops of archaeological interest ofthe Mediterranean area (Lipari, Pantelleria, Sardinia, Palmarola and the Greek islands ofMelos and Gyali), were analysed with the normal procedures used in rock analysis by XRF(crushing, powdering and pelletizing). The non-destructive XRF analysis was insteadconducted on splinters taken from the original geological pieces, with the shape deliberatelyworked to be similar to the refuse usually found at archaeological sites. Since the analysiswas conducted on the raw geological fragment, intensity ratios of the suitably selectedchemical elements were used, instead of their absolute concentrations, to avoid surfaceeffects due to the irregular shape. The comparison between concentration ratios (obtainedby traditional XRF methods) and the intensity ratios of the selected trace elements (obtainedfrom the non-destructive methodology) show that the different domains of the chemicalcomposition, corresponding to the geological obsidians of the source areas, are perfectlyequivalent. In the same way, together with the geological splinters, complete archaeologicalobsidians, from Neolithic sites, may be analysed and their provenance may be determined.The proposed non-destructive method uses the XRF method. Due to its sensitivity, low costand high speed, it is surely an extremely valid instrument for the attribution of theprovenance of the archaeological obsidian from Neolithic sites.