Properties of Rocks and Minerals - The Electrical Conductivity of Rocks, Minerals, and the Earth

The electrical conductivity of mantle and transition-zone minerals is known with reasonable precision and can be used to model the deep Earth. In olivine, small polarons (Fe³⁺ on an Mg-site) and magnesium vacancies govern the conductivity at oxygen fugacities of the mantle. Their relative importance varies with temperature; small polarons dominate at lower temperatures with magnesium vacancies playing a greater role at higher temperatures. The dominant conducting species at low oxygen fugacity are less well constrained. Multianvil high-pressure electrical conductivity measurements of mantle and transition-zone minerals (olivine, pyroxene, wadsleyite, ringwoodite, ilmenite, and perovskite) indicate that polarons also govern conductivity in these materials. Hydrogen in these minerals greatly enhances electrical conductivity but the conduction occurs by a mechanism different from that of hydrogen diffusion. Mineral physics-based mantle-conductivity models constructed to fit resistivity and phase results of magnetotelluric studies offer the potential for mapping hydrogen in the mantle and other phases or species that cause high conductivity.