A comparative study of the thermal behaviour of length-fast chalcedony, length-slow chalcedony (quartzine) and moganite

Schmidt, Patrick; Slodczyk, Aneta; Léa, Vanessa; Davidson, Anne; Puaud, Simon; Sciau, Philippe

doi:10.1007/s00269-013-0574-8

Cited by 30 publications

(24 citation statements)

References 22 publications

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“…However, no porosity increase upon heating has so far been identified in silcrete from the Cape coastal zone [7, 8]. Increasing pore space in silica rocks upon heating was previously assigned to internal fracturing [7, 8, 34, 44, 48, 49]; its dramatic increase in our Kalahari samples suggests intense fracturing upon heat treatment at relatively low temperatures. The mechanism behind such fracturing is the critical steam pressure of trapped H 2 O [46, 49] that is produced by reaction (1) and that cannot be evacuated through open pores [50].…”

Section: Discussionmentioning

confidence: 59%

Heat treatment as a universal technical solution for silcrete use? A comparison between silcrete from the Western Cape (South Africa) and the Kalahari (Botswana)

et al. 2017

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Heat treatment was one of the first transformative technologies in the southern African Middle Stone Age (MSA), with many studies in the Cape coastal zone of South Africa identifying it as an essential step in the preparation of silcrete prior to its use in stone tool manufacture. To date, however, no studies have investigated whether heat treatment is necessary for all silcrete types, and how geographically widespread heat treatment was in the subcontinent. The aim of this study is to investigate experimentally whether heat treatment continued further north into the Kalahari Desert of Botswana and northernmost South Africa, the closest area with major silcrete outcrops to the Cape. For this we analyse the thermal transformations of silcrete from both regions, proposing a comprehensive model of the chemical, crystallographic and ‘water’-related processes taking place upon heat treatment. For the first time, we also explore the mobility of minor and trace elements during heat treatment and introduce a previously undescribed mechanism—steam leaching—causing depletion of a limited number of elements. The results of this comparative study reveal the Cape and Kalahari silcrete to respond fundamentally differently to heat treatment. While the former can be significantly improved by heat, the latter is deteriorated in terms of knapping quality. These findings have important implications for our understanding of the role of fire as a technical solution in MSA stone tool knapping, and for the extension of its use in southern Africa. Silcrete heat treatment—at least in the form we understand it today—may have been a strictly regional phenomenon, confined to a narrow zone along the west and south coast of the Cape. On the basis of our findings, silcrete heat treatment should not be added as a new trait on the list of behaviours that characterise the MSA of the southern African subcontinent.

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Section: Discussionmentioning

confidence: 59%

Heat treatment as a universal technical solution for silcrete use? A comparison between silcrete from the Western Cape (South Africa) and the Kalahari (Botswana)

et al. 2017

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“…Within chalcedony and other microcrystalline silica varieties between 5 and 20 wt % of moganite may crystallize (Heaney and Post, 1992). Raman spectroscopy investigations performed on SiO 2 samples from hydrothermal deposits, cherts, and flints have demonstrated that moganite in microcrystalline quartz/chalcedony can be detected (Kingma and Hemley, 1994;Hopkinson et al, 1999;Götze et al, 1998Götze et al, , 1999Rodgers and Cressey, 2001;Rodgers and Hampton 2003;Pop et al, 2004;Rodgers et al, 2004;Heaney et al, 2007;Schmidt et al, 2012Schmidt et al, , 2013Sitarz et al, 2014). Results show that the main Raman bands are located at 462-465 and 500-503 cm −1 for α-quartz and chalcedony with different wt % of moganite, respectively.…”

Section: Raman Spectroscopymentioning

confidence: 99%

Feathery and network-like filamentous textures as indicators for the re-crystallization of quartz from a metastable silica precursor at the Rusey Fault Zone, Cornwall, UK

Yilmaz

Duschl²,

Genova

2016

Solid Earth

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Abstract. Hydrothermal quartz crystals, which occur in the Rusey Fault Zone (Cornwall, UK), show feathery textures and network-like filamentous textures. Optical hot-cathodoluminescence (CL) analysis and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) investigations on quartz samples revealed that positions exhibiting feathery textures (violet luminescence) contain higher amounts of Al and Li than quartz positions without feathery textures (blue luminescence), while concentrations of Al and Li are significantly lower in feathery textures. Both Al and Li correlate negatively with Si. Raman spectroscopy investigations revealed the presence of a weak peak at 507–509 cm−1 in quartz affected by feathery textures, which we attribute to the presence of ≤  5 % moganite, a microcrystalline silica polymorph, intergrown with chalcedony. The combined occurrence of feathery textures and network-like filamentous textures in quartz samples from the Rusey Fault Zone points to the presence of a metastable silica precursor (i.e., amorphous silica or silica gel) before or during the crystallization.

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“…(); similarly, silicates are affected at about 550°C (Deal ), obsidian in the range of 500–600°C (Deal ), silcrete at over 600°C (Mercieca and Hiscock ), basalt starting at 400°C (Deal ), mudstone at more than 500°C (Mercieca and Hiscock ) and LS–LF chalcedony at over 450°C (Schmidt et al . 2013a,b). Thus, pot lids provide unmistakable evidence of fire exposure, while signs that appear at lower temperatures (such as colour and surface alterations) are more ambiguous and harder to identify.…”

Section: Methodsmentioning

confidence: 99%

Thermoluminescence Dating of Surface Lithic Artefacts from the Chacabuco Valley, Chilean Patagonia

et al. 2013

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This work presents several thermoluminescence (TL) dates of six archaeological sites located in the Andean valley of the Chacabuco River, central Patagonia. We discuss the advantages of this method to assess the chronology of human occupations, employing samples of lithic artefacts with evidence of fire exposure from surface contexts in the area. We compare the results with stratigraphic archaeological dating by 14C. We discuss these results in the context of previously formulated hypotheses on the past behaviour of the human population in this area.

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A comparative study of the thermal behaviour of length-fast chalcedony, length-slow chalcedony (quartzine) and moganite

Cited by 30 publications

References 22 publications

Heat treatment as a universal technical solution for silcrete use? A comparison between silcrete from the Western Cape (South Africa) and the Kalahari (Botswana)

Heat treatment as a universal technical solution for silcrete use? A comparison between silcrete from the Western Cape (South Africa) and the Kalahari (Botswana)

Feathery and network-like filamentous textures as indicators for the re-crystallization of quartz from a metastable silica precursor at the Rusey Fault Zone, Cornwall, UK

Thermoluminescence Dating of Surface Lithic Artefacts from the Chacabuco Valley, Chilean Patagonia

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