Microscopic analysis of technical and functional traces as a method for the use-wear analysis of rock crystal tools

Rock crystal is a high-quality quartz variety with an excellent aptitude for knapping. Although it is relatively uncommon, in certain geological contexts such as that of our case study, rock crystal can serve as the raw material for a substantial number of tools. Nevertheless, very little research has been devoted to the study of this material. This lack of interest may stem from a variety of sources, from the difficulty of analysing a translucent material to its direct attachment to the symbolic world. Here we propose a methodology for the microscopic analysis of rock crystal artefacts in order to establish a better approach for understanding the functionality of this raw material. We comprehensively analysed a series of experimental tools before use by means of different microscopic equipment (OLM with a Nomarski prism and SEM). After the initial documentation, the tools were used in a sequential experimental programme in order to monitor and document the development of use-wear traces. Fourteen experiments were conducted on different materials and with different actions in which the different use traces as well as their respective orientations and sizes were recorded over a series of established times. The set of experiments resulted in different associations of use-wear traces (striations, chipping, rounding and polish) characteristic of the various worked materials and actions employed. We also documented how a technical mark such as the lancet can provide functional information. This is due to the formation process of the mark by percussion or pressure. While lancets formed from the impact point on the ventral side are distributed radially, those created by flake removal follow the kinematics of the tool. Finally, we demonstrated that rock crystal is a material that offers great possibilities for use-wear analyses once a set of technical and functional associations of mark analyses have been determined. Furthermore, although OLM with a Nomarski prism proved to be highly suitable in the analysis of rock crystal, its combination with other techniques such as SEM can provide additional information.