Petrographic and spectroscopic (FT-IR) study of Western Mediterranean obsidians geological sources and of a lithic collection from Ustica Island (Sicily)

Abstract

In this study we applied petrochemical methods (SEM-EDS; FT-IR) in order to characterize a group of obsidian flakes collected at Ustica island (Sicily). Despite the absence of obsidian geological outcrops, a lot of obsidian fragments still emerging from the lands of Ustica testify that the island was a major import center of obsidian during the prehistory. On this island, there are some prehistoric settlements, dated from the Neolithic to the Middle Bronze Age (6000- 1200 BC), in which the use of obsidian continued until the beginning of metals age. Our study includes: i) Macroscopic and microscopic optical observations, which allowed selecting 18 obsidian flakes (starting from 50 obsidian flakes) on the base of their morphological characteristics. ii) Density measurements (hydrostatic balance). iii) Scanning electron microscope determination (SEM-EDS) of major elements of the obsidian glasses and minerals. Results of our analyses were compared with 12 geological samples collected in obsidian sources from Monte Arci (Sardinia), Palmarola, Lipari and Pantelleria, i.e. the four most exploited obsidian sources of the ancient world in the Western-Central Mediterranean. This study confirms the presence of the Lipari and Pantelleria sources (Sicily) in our obsidian set. iv) We also determined (by FT-IR) the hydration degree of some obsidian flakes in order to detect a possible hydration gradient between the rim and the core of the flake sample. The width of the hydration rim, if any, can be used for an approximate evaluation of the age of the tool.