Bone mineral is structurally related to the naturally occurring geologic mineral, hydroxyapatite (HA), differing in crystal size, perfection, and the nature of included impurities. Wide-angle X-ray diffraction (XRD) shows bone mineral diffraction maxima at the same positions as those of HA, but the peaks are less sharp and broader (Fig. 1). This broadening is attributable to the small size of the bone mineral crystals, and to the inclusion of vacancies and impurities (e.g., Mg+2, Sr+2, CO3−2, HPO4−2, etc) in the HA crystal lattice. The presence of these impurities has been demonstrated by chemical analysis of bone homogenates and by magic angle spinning nuclear magnetic resonance (NMR) of bones of various ages [1]. Infrared spectroscopy also shows the presence of carbonate and acid phosphates in homogenized bone. More recently, Fourier transform infrared (FTIR) microscopy was used to characterize bone mineral (and matrix) with a spatial resolution of 6 μm to 10 μm [2].
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