Skip to main content
placeholder image

Experimental heat treatment of silcrete implies analogical reasoning in the Middle Stone Age

Journal Article


Abstract


  • Siliceous rocks that were not heated to high temperatures during their geological formation display improved knapping qualities when they are subjected to controlled heating. Experimental heat treatment of South African silcrete, using open fires of the kind used during the Middle Stone Age, shows that the process needed careful management, notwithstanding recent arguments to the contrary. Silcrete blocks fractured when heated on the surface of open fires or on coal beds, but were heated without mishap when buried in sand below a fire. Three silcrete samples, a control, a block heated underground with maximum temperature between 400 and 500°C and a block heated in an open fire with maximum temperature between 700 and 800°C, were analysed with X-ray powder diffraction (XRD), X-ray fluorescence (XRF), optical microscopy, and both Fourier transform infrared (FTIR) and Raman spectroscopy. The results show that the volume expansion during the thermally induced α- to β-quartz phase transformation and the volume contraction during cooling play a major role in the heat treatment of silcrete. Rapid heating or cooling through the phase transformation at 573°C will cause fracture of the silcrete. Successful heat treatment requires controlling surface fire temperatures in order to obtain the appropriate underground temperatures to stay below the quartz inversion temperature. Heat treatment of rocks is a transformative technology that requires skilled use of fire. This process involves analogical reasoning, which is an attribute of complex cognition.

UOW Authors


  •   Wadley, Lyn (external author)
  •   Prinsloo, Linda (external author)

Publication Date


  • 2014

Citation


  • Wadley, L. & Prinsloo, L. C. (2014). Experimental heat treatment of silcrete implies analogical reasoning in the Middle Stone Age. Journal of Human Evolution, 70 (1), 49-60.

Scopus Eid


  • 2-s2.0-84899129871

Ro Metadata Url


  • http://ro.uow.edu.au/smhpapers/3652

Has Global Citation Frequency


Number Of Pages


  • 11

Start Page


  • 49

End Page


  • 60

Volume


  • 70

Issue


  • 1

Place Of Publication


  • United Kingdom

Abstract


  • Siliceous rocks that were not heated to high temperatures during their geological formation display improved knapping qualities when they are subjected to controlled heating. Experimental heat treatment of South African silcrete, using open fires of the kind used during the Middle Stone Age, shows that the process needed careful management, notwithstanding recent arguments to the contrary. Silcrete blocks fractured when heated on the surface of open fires or on coal beds, but were heated without mishap when buried in sand below a fire. Three silcrete samples, a control, a block heated underground with maximum temperature between 400 and 500°C and a block heated in an open fire with maximum temperature between 700 and 800°C, were analysed with X-ray powder diffraction (XRD), X-ray fluorescence (XRF), optical microscopy, and both Fourier transform infrared (FTIR) and Raman spectroscopy. The results show that the volume expansion during the thermally induced α- to β-quartz phase transformation and the volume contraction during cooling play a major role in the heat treatment of silcrete. Rapid heating or cooling through the phase transformation at 573°C will cause fracture of the silcrete. Successful heat treatment requires controlling surface fire temperatures in order to obtain the appropriate underground temperatures to stay below the quartz inversion temperature. Heat treatment of rocks is a transformative technology that requires skilled use of fire. This process involves analogical reasoning, which is an attribute of complex cognition.

UOW Authors


  •   Wadley, Lyn (external author)
  •   Prinsloo, Linda (external author)

Publication Date


  • 2014

Citation


  • Wadley, L. & Prinsloo, L. C. (2014). Experimental heat treatment of silcrete implies analogical reasoning in the Middle Stone Age. Journal of Human Evolution, 70 (1), 49-60.

Scopus Eid


  • 2-s2.0-84899129871

Ro Metadata Url


  • http://ro.uow.edu.au/smhpapers/3652

Has Global Citation Frequency


Number Of Pages


  • 11

Start Page


  • 49

End Page


  • 60

Volume


  • 70

Issue


  • 1

Place Of Publication


  • United Kingdom