Rainbow in the dark. The identification of diagnostic projectile impact features on rock crystal

Over the last years, functional analyses and projectile fracture analyses on non-chert tools are becoming widespread and are drawing more attention in the archaeological literature. The actual tendencies of conducting holistic studies of the archaeological sites and their materials is allowing to obtain a better quality of data and a better understanding of the subsistence patterns of hunter-gatherer societies. In this way, rock crystal and other types of minerals and rocks of the quartzose group are getting a significant presence in the literature. In this paper, we intend to address a comprehensive approach, both macroscopic and microscopic, to an assemblage of experimental rock crystal projectiles to shed light on the identification of the diagnostic features of the use of small rock crystal pieces as projectile points. Aiming to avoid misidentifications, we did not only follow a sequential experiment design, but also carried out a comparative analysis between impact fractures and knapping fractures, marks from bipolar knapping on an anvil, and intentional bending fractures. Besides, in the elaboration of the experimental projectile assemblage we used different sets of targets to document possible differences in the quantity and disposition of the wear impact traces. This research is framed in the PGC2018-093925-B-C32 (MICINN-FEDER), the 2017SGR1040 and 2017SGR836 (AGAUR) and the 2018PFR-URV-B2-91 (URV) projects. Research at IPHES is framed in the CERCA program. J.L.F.M. is beneficiary of PhD research fellowship FPI MINECO/FSE (BES-2015-074931) associated with the MINECO project HAR2014-55131. D.L. is a beneficiary of PhD research fellowship AGAUR/FSE “L’ FSE inverteix en el teu futur” (2020 FI_B2 00164). R.H. is a beneficiary of a PhD research fellowship URV-Martí-Franquès Research Grant (2019PMF-PIPF-59). I.C. is beneficiary of a PEJ grant (PEJ2018-005226-P) funded by the Spanish National System of Garantía Juvenil and the European Social Fund.