An x-ray study of the paracrystalline nature of bone apatite.

X-ray diffraction from oriented bone sections show that the crystalline apatite content of untreated mature cortical bovine bone has, in fact, a paracrystalline structure (i.e., no long range order). There is anisotropy in both lattice distortions and the sizes of the coherently diffracting domains. The paracrystalline mean distance fluctuations (g) were found to be 1.5 (+/- 0.1)% and 2.9 (+/- 0.2)% for the basal and prism planes respectively, the corresponding paracrystalline sizes being 220 (+/- 20) and 70 (+/- 10) A. The paracrystalline structure became more ordered above 600 degrees C, suggesting the association of hydroxyl and possibly carbonate and other ions with the paracrystalline structure. The paracrystalline model for bone apatite helps explain anomalies between X-ray and electron microscope measurements of crystal size and also more of the biological functions of the crystalline apatite.