Electrical conductivity of phlogopites at high temperatures

Geoelectric properties of phlogopites are studied in the interval 100-1000 degrees C. The main characteristic of the electrical conductivity (sigma) dependence on absolute temperature T, log sigma =f(1/T), is the presence of three main regions: the region of impurity conductivity controlled by the existence of lattice defects associated into complexes; the region above approximately 800 degrees C, where these complexes are completely dissociated; and the region above about 900 degrees C, controlled by the intrinsic mechanism of electric ion transfer. The values of the electrical conduction activation energy and the preexponential factor are determined for all these regions, which is very important because of a significant role of associated defects in metamorphic processes in minerals and rocks. The relation between variations in electrical conductivity, dehydroxylation in the octahedral layer of phlogopites, and variations in the composition of isomorphic cations in the mica structure is established.