SINGLE-CRYSTAL ELASTIC-CONSTANTS OF FLUORAPTITE, CA5F (PO4)3

The single-crystal elastic stiffnesses of fluorapatite, Ca5F(PO4)3, ha ve been measured by an ultrasonic technique. The values are: C-11=152. 0, C-12=49.99, C-13=63.11, C33=185.7, and C44 = 42.75 GPa. These resul ts are compared with previously published values to resolve anisotropy contradictions and differences in-magnitude. The apatite crystal stru cture is not very elastically anisotropic. It suggests that the elasti c anisotropy of bone derives primarily from the hierarchical microstru cture of that biocomposite and not from the anisotropy contribution of the apatite mineral component.