Detailed near-infrared study of the ‘water’-related transformations in silcrete upon heat treatment
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- 作者：Patrick Schmidt ; Christoph Lauer ; Gerald Buck…
- 关键词：Lithic heat treatment ; Thermal transformations ; Silica rocks ; Near FTIR ; South African silcrete MSA heat treatment
- 刊名：Physics and Chemistry of Minerals
- 出版年：2017
- 出版时间：January 2017
- 年：2017
- 卷：44
- 期：1
- 页码：21-31
- 全文大小：
- 刊物类别：Earth and Environmental Science
- 刊物主题：Mineralogy; Crystallography and Scattering Methods; Geochemistry; Mineral Resources;
- 出版者：Springer Berlin Heidelberg
- ISSN：1432-2021
- 卷排序：44
文摘
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.