Evaluation of ATR-FTIR spectroscopy for distinguish anthropogenic and geogenic calcite.

Abstract

Infrared spectroscopy allows to reliably distinguish between calcites formed by different processes, e.g. geogenic and anthropogenic calcite. This approach can be used for rapid sample analysis in the radiocarbon dating of mortars. The datable component is represented by anthropogenic calcite, that results from the reaction of calcium hydroxide with the atmospheric CO2 during the hardening of the material. However, different possible sources of contamination can alter the true radiocarbon concentration and can thus make the mortar appearing either older or younger. The preventive identification of the origin of calcite present in the sample allows to measure only anthropogenic calcite, reducing the time and cost of Accelerator Mass Spectrometer (AMS) measurements. Many papers are present in the literature discussing the use of Fourier transform infrared spectrometry (FTIR) with the KBr pellet method, to distinguish the origin of calcite. In this paper, the use of attenuated total reflectance mode (ATR-FTIR) is evaluated since it may present valuable advantages such as non-destructivity, in the perspective of sample reuse for dating.