FTIR-Based crystallinity assessment of aragonite-calcite mixtures in archaeological lime binders altered by diagenesis

Michael B. Toffolo, Lior Regev, Stéphan Dubernet, Yannick Lefrais, Elisabetta Boaretto

Research output: Contribution to journalArticlepeer-review

49 Scopus citations

Abstract

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.

Original languageEnglish
Article number121
JournalMinerals
Volume9
Issue number2
DOIs
StatePublished - Feb 2019
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2019 by the authors. Licensee MDPI, Basel, Switzerland.

Keywords

  • Aragonite
  • Calcite
  • Carbonate
  • Diagenesis
  • FTIR
  • Lime
  • Mortar
  • Plaster
  • Radiocarbon
  • XRD

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