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The AAPG/Datapages Combined Publications Database
It is well known that measurement of magnetic anisotropy indicates the dimensional grain fabric of natural rocks. Although the directional results are easily interpreted, the quantitative descriptive parameters of the magnetic fabric require more care--but they can give valuable information as to the nature of the grain fabric. In direct grain-shape-related magnetic anisotropy, e.g., in magnetite, it is possible to compare magnetic and optical fabric results by using a density function to describe the distribution of the dimensional axes of an aggregate of similar particles. The data are tested with sand deposited at the angle of repose. By using this method to produce a standard depositional
mechanism, it is seen that the magnetic fabric resulting from magneto-crystalline anisotropy within particles such as hematite has similar directional properties, but the descriptive parameters differ from the magnetite example. In natural sedimentary rocks the source mineral grains causing the magnetic fabric are more elusive. Nevertheless, simple deposition tests with crushed samples confirm that the directional data are correct. Also the descriptive parameters can be used to distinguish between primary and various deformational fabrics.
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