Calcium environment in bone mineral determined by EXAFS spectroscopy.

Extended X-ray absorption fine structure (EXAFS) spectra were recorded, above the Ca K edge, from powdered mouse femurs. Spectra were interpreted on the basis of a model developed previously to explain the features of the EXAFS spectrum of fully crystalline hydroxyapatite. Eight shells of atoms surrounding Ca out 0.57 nm were required to explain the appearance of the EXAFS spectrum of bone. Shell radii and Debye-Waller factors were systematically varied to obtain the best fit between observed and theoretical spectra, calculated using exact spherical wave theory. The results were closely similar to those obtained previously from the interpretation of EXAFS spectra from poorly crystalline hydroxyapatite prepared by maturation of amorphous calcium phosphate. However, there appears to be slightly more disorder in bone mineral, perhaps as a result of its accommodating carbonate ions.