Stability of Remanent Magnetization of Igneous Rocks

Abstract

Most tests of the magnetic stability of a rock provide only a crude evaluation. A better estimation could be obtained by measuring the spectrum of coercivities possessed by a rock; a simple means of obtaining the coercivity spectrum is presented. It is also shown that a relation between the distribution of grain size and the spectrum of coercivities exists, not only for prepared samples, but for rocks as well. An evaluation of the sizes of the opaque grains effectively controlling the magnetic properties must not only take account of initial crystallization processes but must include consideration of post-consolidation, high- and low-temperature oxidation modifications. The development of effective grain size is discussed. Results of this study have provided additional insight into the relation of the shape of a Js-T curve and the opaque mineralogy.