Magnetic Anisotropy

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The magnetic properties of rocks and minerals are generally anisotropic, that is, they are directionally dependent. Magnetic anisotropy of minerals arises from either fundamental anisotropy in the crystal structure or from the shape of nonspherical ferromagnetic grains. The most common cause of magnetic anisotropy in rocks is the preferential distribution-orientation of the constituting minerals, in other words the rock fabric.


Pioneering works on the magnetic anisotropy of rocks were carried out during the 1940s and 1950s (Ising, 1942; Graham, 1954). These authors first realized that magnetic methods may be used to characterize the preferred orientation of minerals within the rock samples. Ising studied varved clays in Sweden and noticed that the magnetic susceptibility was higher on the bedding plane than orthogonally to it. Graham recognized that the anisotropy of magnetic susceptibility (AMS) may be regarded as a petrofabric element; he la