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FTIR-Based Crystallinity Assessment of Aragonite–Calcite Mixtures in Archaeological Lime Binders Altered by Diagenesis

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Institut de Recherche sur les Archéomatériaux-Centre de Recherche en Physique Appliquée à l’Archéologie (IRAMAT-CRP2A), UMR 5060 CNRS, Université Bordeaux Montaigne, 8 Esplanade des Antilles, 33607 Pessac, France
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D-REAMS Radiocarbon Dating Laboratory, Weizmann Institute of Science, 234 Herzl Street, Rehovot 7610001, Israel
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Author to whom correspondence should be addressed.
Minerals 2019, 9(2), 121; https://doi.org/10.3390/min9020121
Received: 10 January 2019 / Revised: 13 February 2019 / Accepted: 15 February 2019 / Published: 18 February 2019
Lime plaster and mortar are pyrotechnological materials that have been employed in constructions since prehistoric times. They may nucleate as calcite and/or aragonite under different environmental settings. In nature, aragonite and calcite form through biogenic and geogenic processes that lead to different degrees of atomic order. The latter is a result of defects in the crystal lattice, which affect the properties of crystals, including their interaction with infrared light. Using Fourier transform infrared spectrometry (FTIR) with the KBr pellet method, it is possible to exploit these differences and assess the degree of atomic order of aragonite and calcite crystals and thus their mechanisms of formation. Here we use FTIR to characterize the degree of short-range atomic order of a pyrogenic form of aragonite recently observed in experimental and archaeological lime binders. We show that pyrogenic aragonite has a unique signature that allows its identification in archaeological sediments and lime binders of unknown origin. Based on these results, we developed a new FTIR-based method to assess the integrity and degree of preservation of aragonite and calcite when they occur together in the same material. This method allowed a better assessment of the diagenetic history of an archaeological plaster and finds application in the characterization of present-day conservation materials, such as lime plaster and mortar, where different polymorphs may nucleate and undergo recrystallization processes that can alter the mechanical properties of binders. View Full-Text
Keywords: lime; plaster; mortar; carbonate; calcite; aragonite; radiocarbon; FTIR; XRD; diagenesis lime; plaster; mortar; carbonate; calcite; aragonite; radiocarbon; FTIR; XRD; diagenesis
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Toffolo, M.B.; Regev, L.; Dubernet, S.; Lefrais, Y.; Boaretto, E. FTIR-Based Crystallinity Assessment of Aragonite–Calcite Mixtures in Archaeological Lime Binders Altered by Diagenesis. Minerals 2019, 9, 121.

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