The physical theory of rock magnetism

Abstract

Abstract Magnetite and hematite are representative of the ferrimagnetic and weakly ferromagnetic minerals which are responsible for the magnetic properties of rocks reviewed in this paper. Magnetite grains are multi-domains in the size range of interest (0.1 μ–1000 μ), whereas hematite grains in the same size range are almost certainly single domains. Properties discussed are coercivity, susceptibility, magnetic viscosity, thermo- and isothermal remanence, alternating field demagnetization, anhysteretic, chemical and detrital magnetization, anisotropy, piezomagnetic effects and self-reversals. Problems requiring more experimental data are emphasized, especially the basal plane anisotropy of hematite, the Barkhausen discreteness of domains in magnetite and the possibility that grains of cubic minerals may have some uniaxial character arising from grain shape or internal strains.