The electrical conductivity of olivine under highly reducing conditions

The electrical conductivity of San Carlos olivine has been measured at 1100 degrees C under reducing conditions at controlled oxygen fugacity, inside and outside the olivine stability field, in order to study the kinetics of olivine destabilization. Electrical conductivity increases along the direct ion [010] and decreases along [001]. as oxygen fugacity decreases. To under stand these f(O2) dependences, electrical conductivity transitory regimes w ere studied. In response to decreases in oxygen fugacity, two transient reg imes with different time scales have been observed. A fast (approximate to 1-2 min) increase of electrical conductivity is first observed, followed by a slower decrease (1-10 h, depending on the crystal orientation). After a few hours of annealing, precipitation of metallic iron and nickel and forma tion of amorphous silica can be observed at the crystal surface. The fast c onductivity increase in the first transient regime is ascribed to an increa se in the population of electrons at the olivine surface. Two effects: (1) equilibration of surface defects with the bulk of the crystal, and (2) iron loss from the olivine due to metal precipitation, could explain the subseq uent decrease of electrical conductivity. Anisotropic diffusion of surface defects to the bulk of the crystal, by a process faster than atomic diffusi on is the most likely.