Early Diagenetic Evolution of Bone Phosphate: An X-ray Diffractometry Analysis

A new crystallinity index (CI), based on the X-ray powder diffractometric pattern of fossil bone carbonate hydroxylapatite, is defined. This CI value provides a semi-quantitative way to estimate the diagenetic changes in archaeological and palaeontological bone phosphate. The studied samples are 71 human bones from the French merovingian cemetery of Saint-Linaire (1200-1700 bp), 37 human bones from two necropoleis in Niger (1000-5000 bp), two cave bear bones from Aldène Cave (southern France; around 70,000 bp), five bones of Miocene mammals and 14 bones of Mesozoic reptiles. The main results are that: (1) there is no correlation between the increase in the CI and the age of the sample, even in one given locality; (2) the CI seems to be related to the taphonomical conditions, in archaeological and fossil bones; (3) an increase in the CI is correlated with a loss in organic matter in one archaeological site, but the quality of preservation of organic matter in fossil bones does not depend on the changes in the CI; (4) the correlation between the increase in the CI and the decrease of CO 3amount in bones from the Niger necropolies suggests a possible mechanism for the increase in crystallinity. The changes of crystallinity reflect early diagenetic changes and depend on the burial environments.