Heat treatment of silcrete raw materials: the implications of temperature-induced transformations for archaeological provenancing studies

Establishing the source of raw material used in stone tool manufacture can provide insights into the development of a range of human behavioural traits, including mobility. Working in Botswana, the PI developed a novel geochemical provenancing approach for silcrete (a type of silica-cemented duricrust with flint-like properties) and identified that it was transported up to 295km during the Middle Stone Age (MSA).

The approach has the potential to be applied at South African MSA sites. An issue, however, is whether it needs modification for stone that was heat-treated prior to knapping, a widespread practice during the MSA. We aim to use an experimental approach to establish the impact of heat-treatment upon silcrete chemistry.

We use techniques including near- and mid-infrared (NIR, mid-IR), x-ray diffraction (XRD), inductively-coupled plasma mass spectrometry (ICP-MS) and atomic emission spectroscopy (ICP-AES) on heated and unheated samples. Our results seek to demonstrate how, and at what temperature, chemical transformations occur, with implications for future provenancing work.

Results from the project have been published in two papers:

Schmidt, P., Nash, D.J., Coulson, S., Göden, M.B. & Awcock, G.J. (2017) Heat treatment as a universal technical solution for silcrete use? A comparison between silcrete from the Western Cape (South Africa) and the Kalahari (Botswana). PLoS ONE 12: e0181586.

Nash, D.J., Coulson, S. & Schmidt, P. (2019) Heat treatment of Kalahari and Cape silcretes: impacts upon silcrete chemistry and implications for geochemical provenancing. Archaeological and Anthropological Sciences 11: 6865-6874.