In this paper we develop a model for ionic transport in forsterite which predicts a different directional dependence of transport for magnesium interstitials and vacancies. This model, together with dc transport measurements on forsterite into which iron was diffused, suggests that we are dealing with interstitial transport in synthetic forsterite, whereas diffusion experiments on olivine reported in the literature have been dealing with vacancy transport. Our transport measurements also support the idea that ${\mathrm{Fe}}^{3+}$ acts as an acceptor level lying 3.0 eV above the valence band of forsterite. Transport measurements are also reported for forsterite into which hydrogen has been diffused.

• Received 6 September 1978

DOI:https://doi.org/10.1103/PhysRevB.19.2886