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Nucleation of aragonite upon carbonation of calcium oxide and calcium hydroxide at ambient temperatures and pressures: a new indicator of fire-related human activities

Toffolo, Michael B. ; Boaretto, Elisabetta

Journal of archaeological science, 2014-09, Vol.49, p.237-248 [Periódico revisado por pares]

Kidlington: Elsevier Ltd

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  • Título:
    Nucleation of aragonite upon carbonation of calcium oxide and calcium hydroxide at ambient temperatures and pressures: a new indicator of fire-related human activities
  • Autor: Toffolo, Michael B. ; Boaretto, Elisabetta
  • Assuntos: Analysis of archaeological features ; Analytical chemistry ; Aragonite ; Archaeology and Prehistory ; Calcite ; Chemical Sciences ; Cristallography ; Earth Sciences ; Fire ; FTIR ; Geochemistry ; Humanities and Social Sciences ; Inorganic chemistry ; Lime plaster ; Material chemistry ; Methodology and general studies ; Microarchaeology ; Mineralogy ; Prehistory and protohistory ; Pyrotechnology ; Quicklime ; Sciences of the Universe
  • É parte de: Journal of archaeological science, 2014-09, Vol.49, p.237-248
  • Descrição: Wood ash found at archaeological sites is the most direct evidence of the presence of combustion features. The preservation of wood ash within archaeological deposits is often poor due to diagenetic processes and therefore its identification requires the use of spectroscopic methods. FTIR spectrometry is able to detect the main calcite component of wood ash, unless this is mixed with other calcitic phases of geologic origin. Using FTIR spectrometry we identified non-biogenic aragonite in archaeological heat-altered sediments and lime plasters. The presence of aragonite in such conditions is unusual, as it is unlikely to crystallize at ambient temperatures and pressures or in absence of Mg. The experimental conditions which favor the nucleation of this aragonite phase were investigated with FTIR spectrometry, XRPD and SEM imaging of modern lime plaster and quicklime samples prepared in the laboratory using different calcium carbonate starting materials. We show that aragonite forms at ambient temperatures and pressures upon carbonation of calcium oxide and calcium hydroxide together with calcite and its nucleation and growth are influenced by environmental parameters, such as carbon dioxide partial pressure, relative humidity and temperature. This pyrogenic aragonite is a reliable indicator for calcareous materials exposed to temperatures above 600 °C, and therefore it can be used to determine the presence of heat-altered sediments and ash in the absence of structured combustion features. This mineral phase could have applications in radiocarbon dating as well. •Aragonite was found in archaeological ash and lime plaster using FTIR spectrometry.•Quicklime and plaster were prepared to understand the formation of aragonite.•All the tested CaCO3 starting materials produced aragonite together with calcite.•The nucleation of pyrogenic aragonite is driven by environmental parameters.•Pyrogenic aragonite has implications in the study of ancient pyrotechnology.
  • Editor: Kidlington: Elsevier Ltd
  • Idioma: Inglês
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  • Realização: ABCD-USP USP   Logos de Redes Sociais: Freepik

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