Breakage, scarring, scratches and explosions: understanding impact trace formation on quartz

Abstract

Quartz projectiles have received attention in the recent years due to, for instance, their discovery at prominent South African Middle Stone Age sites. However, very few methodological studies have been dedicated to quartz armatures and the ones published so far are not built on an understanding of the particular behaviour of quartz under mechanical stress. Here, we investigate impact damage formation on automorphic and xenomorphic quartz (crystal quartz and vein quartz) through the microscopic analysis of 91 experimental armatures using a combination of low and high magnifications and SEM. Our results show that the structural properties of quartz affect the attributes of impact breaks and other damage. We also examine wear patterns on three different types of projectiles and offer preliminary guidelines for identifying them in archaeological assemblages. We argue that while quartz assemblages withhold significant potential for understanding past hunting technologies, the methods used for identifying and interpreting quartz projectiles need to be adjusted so that they take into account the notable differences between the macrocrystalline and cryptocrystalline varieties of this raw material.