Variations of the mean susceptibility of rocks under hydrostatic and non-hydrostatic pressure

Abstract

Abstract The variations of the mean susceptibility of basaltic rocks and polycrystalline magnetite, measured in weak magnetic field, under external non-hydrostatic (uniaxial) and hydrostatic pressure, are studied. A decrease of the mean susceptibility with increasing pressure was observed in both cases, the changes under uniaxial stress being systematically much larger than those under hydrostatic pressure. These changes are reversible with respect to the application of the external stress. The decrease of mean susceptibility under uniaxial stress is related to the qualitatively different behaviour of the changes of directional susceptibilities of orientations different with respect to the applied stress. The magnitude of the decrease of the actual rocks depends on the ratio of the stress sensitivity constants of the various directional susceptibilities. Small changes of the mean susceptibility under external hydrostatic pressure may be the result of the inhomogeneity of internal stresses acting on ferrimagnetic minerals as a result of the anisotropy of the transmitting properties of the non-magnetic matrix.