Atomic Disorder in Fossil Tooth and Bone Mineral: An FTIR Study Using the Grinding Curve Method

Bone and tooth mineral generally undergo diagenetic changes. These changes in the carbonate hydroxyapatite structure and composition can affect the signals embedded in the mineral phase, such as migration behavior, age of the specimen and the reconstruction of past environments. Mineral preservation state can be assessed using infrared spectroscopy which provides information on crystal disorder at the atomic level and mineral composition. Here we present a new approach to evaluate carbonate hydroxyapatite atomic disorder using infrared spectroscopy and the standard KBr sample mounting method. We show that by repeated grinding of the sample and then plotting the infrared splitting factor against the width of the major phosphate absorption peak after each grinding, grinding curves with well defined trend lines can be obtained. The offsets between curves reflect differences in atomic disorder. We show that grinding curve offsets can be used to evaluate the state of preservation of bone, dentine and enamel mineral.