β-Tricalcium Phosphate Interferes with the Assessment of Crystallinity in Burned Skeletal Remains

Abstract

The analysis of burned remains is a highly complex process, and a better insight can be gained with advanced technologies. The main goal of this paper is to apply X-ray diffraction, partially supported by infrared attenuated total reflectance spectroscopy to determine changes in burned human bones and teeth in terms of mineral phase transformations. Samples of 36 bones and 12 teeth were heated at 1050°C and afterwards subjected to XRD and ATR-IR. The crystallinity index was calculated for every sample. A quantitative evaluation of phases was documented by using the Rietveld approach. In addition to bioapatite, the following mineralogical phases were found in the bone: β-tricalcium phosphate (β-TCP) (Ca3(PO4)2), lime (CaO), portlandite (Ca(OH)2), calcite (CaCO3), and buchwaldite (NaCaPO4). In the case of bone, besides bioapatite, only the first two mineralogical phases and magnesium oxide were present. We also observed that the formation of β-TCP affects the phosphate peaks used for CI calculation. Therefore, caution is needed when its occurrence and evaluation are carried out. This is an important warning for tracking heat-induced changes in human bone, in terms of physicochemical properties related to structure, which is expected to impact in forensic, bioanthropological, and archaeological contexts.

Chemosteometric regression models of heat exposed human bones to determine their pre‐burnt metric dimensions

“…One possible solution to the problem is based on the estimation of metric heat-induced changes by looking at infrared spectroscopic profiles of bone samples. Clear relationships among heat exposure temperature, bone chemometric indices, and heat-induced microstructural changes have been demonstrated previously (e.g., Gonçalves et al, 2018;Hiller, Thompson, Evison, Chamberlain, & Wess, 2003;Lebon et al, 2010;Marques et al, 2016;Munro, Longstaffe, & White, 2007;Piga et al, 2018;Piga, Malgosa, Thompson, & Enzo, 2008;Shipman et al, 1984;Snoeck, Lee-Thorp, & Schulting, 2014;Thompson, Gauthier, & Islam, 2009). Figure 2 illustrates some of these relationships.…”

“…All bands have been used in the past for the calculation of spectroscopic indices except for the 3642 cm −1 signal. This narrow absorption band is due to the stretching mode of OH present in portlandite (Ca[OH] 2 ) (Diallo‐Garcia, Osman, Krafft, Boujday, & Guylène, 2014; Khachani, Hamidi, Halim, & Arsalane, 2014; Menzel & Amberg, 1972) and is found in bones after high temperature treatments (Piga et al, 2018).…”

“…Separation between non‐calcined and calcined bones was done artificially based on the 700°C threshold as a discriminating parameter. It should be noted that this is merely an approximate criterion, since bones burnt at this temperature may not necessarily present the characteristics usually associated to calcination: white coloration, lack of organic matter and crystal size increase (Piga et al, 2018; Thompson, 2004; Walker et al, 2008).…”

“…However, high‐intensity burning causes more variable changes which are therefore much more difficult to address (Figure 1). This considerably complicates the application of osteometric methods to the analysis of calcined skeletal remains, here defined as remains that have usually been submitted to temperatures equal or higher than 700°C, which mostly present a white coloration, contain no organic matter, and show an increase in crystal size (Piga et al, 2018; Thompson, 2004; Thompson, Islam, & Bonniere, 2013; Walker, Miller, & Richman, 2008).…”

Human bone probed by neutron diffraction: the burning process

“…[4][5][6][7][8][9] Heat-induced diagenetic variations in bone have been assessed by several methods, optical (Fourier transform infrared spectroscopy (FTIR) and Raman) and neutron vibrational spectroscopy (inelastic neutron scattering (INS)) having been established as powerful techniques for these types of study. [4][5][6][7][10][11][12][13][14][15][16][17][18][19][20] FTIR spectroscopy in attenuated total reectance mode (FTIR-ATR) is particularly suitable for a daily basis analysis of archaeological or forensic bones since it is easily accessible, inexpensive, fast and requires no specic sample preparation, yielding an accurate chemical and structural prole unique for each sample. Hence, extensive work has been performed by FTIR-ATR on heat-prompted changes in human bone.…”