Effects of composition and high pressures on the electrical conductivity of Fe-rich (Mg, Fe)2SiO4 olivines and spinels

Abstract

Synthetic olivines, with composition Fa50, Fa75 and Fa100, have been transformed into spinel in a laser-heated diamond-cell at pressures from 70 to 200 kbar and at a luminance temperature of about 1,200° C. The electrical conductivity σ was measured, at room temperature and up to 200 kbar, on olivine (Lacam 1982; 1983) and spinel (present study). The data obtained permit the following conclusions: a) Sample nature effect: under the same conditions (composition, pressure), the σ of spinel is more than three orders of magnitude of the σ of olivine. b) Composition effect: there are more than three orders of magnitude between the values of σ for spinels derived from initial compositions of Fa50 and Fa100, respectively. c) Pressure effect: The P-effect on σ is greater for olivines than for spinels.