The study of lithic raw material quality has become one of the major interpretive tools to investigate the raw material selection behaviour and its influence to the knapping technology. In order to make objective assessments of raw material quality, their mechanical properties (e.g., fracture resistance, hardness, modulus of elasticity) should be measured. However, such comprehensive investigations are lacking for the Palaeolithic of Kazakhstan. In this work, we investigate geological and archaeological lithic raw material samples of chert, porphyry, and shale collected from the Inner Asian Mountain Corridor (henceforth IAMC). Selected samples of aforementioned rocks were tested by means of Vickers and Knoop indentation methods to determine one aspect of their mechanical properties: their indentation fracture resistance (a value closely related to fracture toughness). These tests were complemented by traditional petrographic studies to characterise the mineralogical composition and evaluate the level of impurities that could have potentially affected the mechanical properties. The results show that materials, such as porphyry, previously thought to be of lower quality due to the anisotropic composition and coarse feldspar and quartz phenocrysts embedded in a silica rich matrix, possess fracture toughness values that can be compared to those of chert. Thus, it appears that different raw materials cannot be distinguished from the point of view of indentation fracture resistance, calling for detailed supplementary analyses of different fracture properties. This work also offers first insight into the quality of archaeological porphyry that was utilised as a primary raw material at various Middle and Upper Palaeolithic sites in the IAMC.
Mechanical properties of lithic raw materials from Kazakhstan: comparing chert, shale, and porphyry
