Mineralogic Characterisation of Archaeological Bone

Abstract

Isotope studies on archaeological bone mineral require a validation of the material integrity. Diagenetically altered or contaminated bone mineral should be recognized as such and not be used for conclusions requiring pristine material. X-ray diffraction (XRD) and infrared spectroscopy (IR) are two complementary tools that investigate the state of the bone mineral. While modern XRD analysis is based on a direct comparison of observed data with a rigorous quantitative calculation of the diffractogram, the interpretation of the more easily measurable IR data is still largely empirical. We studied a set of archaeological animal bones sampled from the alpine region covering ages from 7600 to 550 years before present. We discarded visually decomposed bones completely. For the remaining samples, we investigated only the central part of the bone; the inner and outer periosteal surfaces were mechanically removed. For these selected samples, the crystalline lattice parameters in the a–b plane of the bioapatite and the average nanocrystallite size in the same plane show a small decreasing trend with age, which is almost insignificant compared to the observed natural variation in the bone apatite. For the c-direction, both the lattice parameter and the crystallite size are constant within this observed variation. We conclude that in the investigated samples there is—if any—only a very minor diagenetic recrystallisation of the original bone mineral.