A single test for raw material properties: hardness and stiffness of tools-stones from Sibhudu

Abstract The study of raw materials used for making stone tools allows archaeologists to gain insight into the behaviours of ancient people. Raw materials possess different properties, which influence the ability of knappers to flake, shape and use a stone tool. Measuring these properties experimentally requires specialised laboratories and measuring processes that are not straightforward. This makes such analyses a cost-intensive and often inaccessible way to investigate the past. Here, we present an alternative way to evaluate two mechanical properties, stiffness and hardness, using a single indentation test. We also test whether these two isolated measures allow making predictions on raw material selection and tool shape. We analysed tool-stones from the Middle Stone Age site Sibhudu on South Africa’s eastern seaboard. The site has yielded a rich assemblage of tools from different raw materials. We found that a single indentation test allows measuring hardness and stiffness reliably, simplifying the measurement protocol of raw material studies. We also observed weak correlations between those isolated properties and the shape of the finished tools. This has implications for future studies of Stone Age raw materials, proposing a simplified testing protocol. We also discuss the role of stiffness in stone knapping.