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Journal of Thermal Analysis and Calorimetry

, Volume 131, Issue 2, pp 1135–1145 | Cite as

The thermal behaviour of silica varieties used for tool making in the Stone Age

  • Linda C. PrinslooEmail author
  • Elizabet M. van der Merwe
  • Lyn Wadley
Article

Abstract

Before 100,000 years ago, during the Middle Stone Age (MSA) of South Africa, silica varieties of minerals and rocks were sometimes heated during tool making in order to improve their knapping properties. If the heating and cooling process is not controlled, failure results and the nodules fracture. Recently, we postulated that the reversible α- to β-phase transition may play a role in causing silcrete, a type of rock often used to make stone tools in the Western Cape, to fracture. In this new study, we analyse the thermal behaviour (520–620 °C) of silcrete and compare it to that of two chalcedony samples from different origins, together with samples of chert, agate and flint. These minerals and rocks were commonly used to make stone tools. Differential scanning calorimetry (DSC) measurements show that the α- to β-phase transformation is prominent in silcrete, agate and one of the chalcedony samples, weaker in chert and the second chalcedony sample, but non-existent in flint. X-ray fluorescence (XRF), thermogravimetric analysis (TG) and carbon and sulphur analyses show differences in elemental composition between the rocks and minerals. X-ray powder diffraction (XRD), Fourier transform infrared (FTIR) and Raman spectroscopy highlight differences in microstructure. These small differences in chemical composition and structure contribute to a variety of chemical reactions and phase transformations that can take place in rocks and minerals, which in combination determine their stability upon heating and show that care should be taken when generalising thermal behaviour.

Keywords

Stone tools Thermal behaviour DSC TG XRF XRD FTIR Raman spectroscopy 

Notes

Acknowledgements

The authors would like to thank Dr. Wiebke Grote and Dr. Jeanette Dykstra from the XRD & XRF Facility, Department of Geology, University of Pretoria, for the XRD and XRF measurements, respectively. We thank Paloma de la Peña for providing the flint sample and G. L. Prinsloo for the digital images of the samples. All the authors acknowledge the National Research Foundation (NRF) for financial support. Opinions expressed in the paper are not necessarily those of the NRF. We thank two anonymous reviewers for useful comments that improved this paper.

Supplementary material

10973_2017_6602_MOESM1_ESM.pdf (623 kb)
Supplementary material 1 (PDF 623 kb)

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Copyright information

© Akadémiai Kiadó, Budapest, Hungary 2017

Authors and Affiliations

  1. 1.Centre for Archaeological Science, School of Earth and Environmental SciencesUniversity of WollongongWollongongAustralia
  2. 2.Department of PhysicsUniversity of PretoriaHatfieldSouth Africa
  3. 3.Department of ChemistryUniversity of PretoriaHatfieldSouth Africa
  4. 4.Evolutionary Studies Institute, and the Centre of Excellence, PalaeosciencesUniversity of the WitwatersrandJohannesburgSouth Africa

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