The time dependence of electrical conductivity following step changes in oxygen fugacity has been used to deduce the diffusivities of the dominant point defects in pyroxene-buffered San Carlos olivine. Nonlinear least squares fits of the data indicate that two relaxation times (&tgr;) are present in the conductivity-time records. The effective diffusivity calculated from the slower &tgr; agrees with values reported for the chemical diffusivity of metal vacancies (V∥Me). The effective diffusivity calculated from the faster &tgr; coincides with that measured for analogous changes in strain rate (ϵ˙ ) following step changes in fO2. This faster diffusivity of silicon vacancies (V∥∥Si). These results imply that defects on the tetrahedral and octahedral sublattices of olivine may reequilibrate independently. Furthermore, changes in electrical conductivity and strain rate resulting from changes in thermodynamic conditions are initiated by reequilibration of the faster of these defects. ¿ American Geophysical Union 1994