Variability of the rebound hardness as a proxy for detecting the levels of continuity and isotropy in archaeological quartz

Abstract

The Equotip Hardness Tester is applied to different types of quartz and other lithic raw materials in order to determine if variations in the rebound hardness measured by this device may serve as a proxy for detecting the levels of continuity and isotropy of toolstones. Continuity, the amount of cracks and other internal defects; and isotropy, the measure of the directional properties of a raw material, are known to have important effects on the level of consistency and predictability of fractures, which in turn is traditionally considered a main factor for defining the flaking quality of a given raw material.The results demonstrate the existence of differences among the raw materials analysed in both the average value and the variability of the rebound hardness. While cryptocrystalline samples show the most homogeneous results, quartz and metamorphic rocks display a comparatively higher variance. In the specific case of quartz, such variability seems to be mainly caused by the presence of internal planes and discontinuities, while anisotropy, although also active, had played a comparatively modest role. The results achieved by the Equotip Hardness Tester suggest that this device could be successfully used for a basic or preliminary estimating of some of the physical and mechanical properties of stone raw materials. Therefore, it is a potential index test for complementing other, more accurate, laboratory methods.