Diffusion of the rare earth in natural and synthetic fluorapatite was characterized under anhydrous conditions. In the case of in-diffusion experiments, apatite was immersed in reservoirs of synthetic REE apatite analogs of various compositions. In out-diffusion experiments, synthetic Nd-doped apatite was immersed in a reservoir of synthetic (undoped) fluorapatite. The depth profiles were measured using Rutherford back-scattering spectrometry. For the in-diffusion experiments, at 800 to 1250C:

D(m2/s) = 2.4 x 10-6 exp[-348(kJ/mol)/RT]

The out-diffusion experiments on Nd-doped synthetic apatite at 950 to 1400C, yielded:

D(m2/s) = 9.3 x 10-6 exp[-392(kJ/mol)/RT]

D.J.Cherniak: Geochimica et Cosmochimica Acta, 2000, 64[22], 3871-85