Distinguishing between calcites formed by different mechanisms using infrared spectrometry: archaeological applications

Abstract

(L. Regev).Keywords: Calcium carbonate, infrared spectroscopy, pyrotechnology, diagenesis, ash, plaster AbstractInfrared spectrometry is a well established method for the identification of minerals. Due to its simplicity and the short time required to obtain a result, it can be practiced on-site during excavation using portable infrared spectrometers. However, the identification of a mineral may not be sufficient. For example, a lime plaster floor and a crushed chalk surface have similar appearance and are composed of the same mineralcalcite. Here we exploit differences in the infrared spectra of geogenic, biogenic and pyrogenic calcites for the identification of each calcite type. The infrared calcite spectrum has three characteristic peaks in the region of 400-4000 cm -1 , designated ν 2 , ν 3 , and ν 4 . Manuscript Click here to view linked References2 When a calcite sample is ground, as part of the measurement preparation procedure, some grinding dependent changes will be revealed in the infrared spectrum. With additional grinding, the ν 3 peak narrows and the heights of the ν 2 and ν 4 peaks decrease, when both are normalized to the ν 3 height. By plotting the normalized heights of the ν 2 versus the ν 4 of several grindings of the same sample, a characteristic trend line is formed for each calcite type. The trend lines of geogenic calcites have the mildest slopes and highest ν 4values when compared to pyrogenic calcites, which can be further divided to ash and plaster/mortar samples. This method can assist in the differentiation of the various calcites, including insights on homogeneity and preservation state of the calcitic materials in question.

Plaster Characterization at the PPNB Site of Yiftahel (Israel) Including the Use of14C: Implications for Plaster Production, Preservation, and Dating

“…This hypothesis is supported by the presence of the fossil foraminifera that would have been recrystallized after complete calcination (Goren and Goldberg 1991). We analyzed all 25 samples with good stratigraphie information using FTIR spectroscopy to compare the atomic order/disorder properties of the calcite crystals from the top layers, the binder, and aggregate material in the lower layers using the grinding curve analysis approach described by Regev et al (2010). The 3 best samples, which are shown in Figure 2, each have a thin top layer that contains calcite that is less crystalline than the calcite contained in the bottom layers.…”

“…In this study, we first assessed the atomic disorder of plaster samples from Yiftahel using infrared spectroscopy (Regev et al 2010;Poduska et al 2011). From these, we selected the 3 best-preserved samples, namely those with disorder signatures most similar to modern plaster.…”

“…Baselines and subsequent peak-height analyses of the v 3 (1420 c m -1 ) , v 2 (874 c m -1 ) , and v 4 (713 c m -1 ) peaks followed procedures in earlier publications (Chu et al 2008). The grinding curve analysis method (Regev et al 2010;Poduska et al 2011) provided information about the degree of crystallinity in different parts of each plaster sample.…”

Another beauty of analytical chemistry: chemical analysis of inorganic pigments of art and archaeological objects

“…45) [85]. It has been observed that there is a correspondence between structural characteristics such as crystallinity and the m 2 /m 4 band intensities ratio as the m 4 band is more influenced by atomic disorder than m 2 band [85][86][87]. Thus, this parameter can be used for discriminating between calcites with different structural characteristics as result of being formed in different conditions.…”

Materials Science Challenges in Radiocarbon Dating: The Case of Archaeological Plasters

“…23,45,46 In general, FTIR peaks will broaden when there are structural differences that influence the local coordination environment in a material. This has been well explored in the case of calcium carbonates through coordinated experimental and theoretical investigations.…”