Physics and Chemistry of Minerals

, Volume 44, Issue 1, pp 21–31 | Cite as

Detailed near-infrared study of the ‘water’-related transformations in silcrete upon heat treatment

  • Patrick SchmidtEmail author
  • Christoph Lauer
  • Gerald Buck
  • Christopher E. Miller
  • Klaus G. Nickel
Original Paper


In archaeology, lithic heat treatment is the process of modifying a rock for stone tool production using fire. Although the earliest known cases of heat treatment come from South Africa and involved silcrete, a microcrystalline pedogenic silica rock, its thermal transformations remain poorly understood. We investigate the ‘water’-related transformations in silcrete using direct transmission near-infrared spectroscopy. We found that SiOH is noticeably lost between 250 and 450 °C and hydroxyl reacts with H2O, part of which is trapped in the structure of the rocks. This water can only be evaporated through heat-induced fracturing at high temperatures, imposing maximum temperatures for silcrete heat treatment of approximately 500 °C. Between 250 and 450 °C new siloxane bonds are formed according to the reaction 2SiOH → Si–O–Si + H2O, which can be expected to transform the rock’s mechanical properties. The tolerance of silcrete for relatively fast ramp rates can be explained by its pore volume and low SiOH content, ensuring good water evaporation. These results shed light on the processes taking place in silcrete during heat treatment and allow for a better understanding of the parameters needed for it.


Lithic heat treatment Thermal transformations Silica rocks Near FTIR South African silcrete MSA heat treatment 



We thank the Deutsche Forschungsgemeinschaft (DFG) for funding of the research project Heat Treatment in the South African MSA that made the present study possible (Grant No: CO 226/25-1, MI 1748/2-1, NI 299/25-1) and for funding the Agilent Cary 660 spectrometer used for parts of this study (MI 1748/1-1). We also thank Junichi Fukuda and an anonymous reviewer for their corrections and suggestions during the review process for this publication.

Supplementary material

269_2016_833_MOESM1_ESM.pdf (527 kb)
Supplementary material 1 (PDF 527 kb)


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Copyright information

© Springer-Verlag Berlin Heidelberg 2016

Authors and Affiliations

  1. 1.Department of Prehistory and Quaternary EcologyEberhard Karls University of TübingenTübingenGermany
  2. 2.Department of Geosciences, Applied MineralogyEberhard Karls University of TübingenTübingenGermany
  3. 3.Institute for Archaeological SciencesEberhard Karls University of TübingenTübingenGermany

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