Argon diffusivities and solubilities in single gem-quality crystals of forsterite were deduced from experiments conducted under 0.5 to ~6000bar Ar pressures at 425 to 1200C. Polished single-crystal slabs and specimens with natural facets were placed in open containers and exposed to an argon atmosphere either in a pressure vessel or in a gas-flow tube furnace at near-atmospheric pressure. Argon atoms from the pressure medium diffused into the crystals to produce near-surface concentration gradients, which were directly profiled using Rutherford back-scattering spectrometry. The following Arrhenius relationships were obtained:

D (m2/s) = 7.2 x 10-20exp[-42(kJ/mol)/RT]

J.B.Thomas, D.J.Cherniak, E.B.Watson: Chemical Geology, 2008, 253[1-2], 1-22