Wear on tools
Obsidian is a silica-rich volcanic glass. Because of its glassy texture it is one of the most homogeneous rocks, with a very low mineral content, less than 5 % in volume (Poupeau et al. 2007). Intra- and inter-sources variations are well known and concern colours, banding, amount of spherulites, mineral contents, geo-chemical composition, magnetic properties and RAMAN structures (Feinberg et al. 2009, Bellot-Gurlet 2003). Variations in the raw material's physical and chemical properties determine the surface topography of the knapped tools, the mechanical behaviour of the artefacts under specific constraints due to use or post-depositional damage (i.e. etching, brittleness, abrasion, striation, development of ‘polishes’). Consequently, as in the case of flint, the variability of obsidian as a raw material has to be taken into account when use-wear analysis is concerned. Wear attributes will develop in a different way on different kind of obsidians.