Reference Work Entry

Encyclopedia of Geomagnetism and Paleomagnetism

pp 535-540

Magnetic Remanence, Anisotropy

  • Ann M. Hirt

It has been known since the early 1950s that rocks and sediments display a magnetic anisotropy when constituent mineral grains have a preferred orientation (Graham, 1954; Hargraves, 1959). Magnetic fabric is usually described by the anisotropy of magnetic susceptibility (AMS), measured in weak applied fields. With this method all minerals in a rock or sediment contribute to the susceptibility. Therefore, the observed anisotropy is the sum of the individual mineral components, their specific susc\eptibility anisotropy and their preferred alignment. Since nonferromagnetic matrix minerals often make up the bulk composition of a rock or sediments, the low‐field susceptibility of these minerals can dominate the measured signal. The anisotropy of magnetic remanence (AMR) is only dependent on the ferromagnetic grains (s.l.) in a rock. Since the number of different ferromagnetic phases is more limited, the source of the AMR is easier to distinguish, and the degree of anisotropy is less sensiti ...

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