Correlation of the petrographic and magnetic properties of the magnetic minerals contained in rocks is least ambiguous when both properties are determined on the same individual mineral grain. Petrographic properties of grains and structures at least as small as 0.05 μm can be obtained from a combination of conventional and modem techniques, including reflected-light microscopy, scanning-electron microscopy, x-ray energy spectrometry, x-ray diffraction analysis, and etching techniques. Our initial results indicate that naturally occurring magnetite commonly contains a rich variety of submicroscopic inclusions and structures, heretofore unobserved, which probably have considerable effect on the magnetic properties of their hosts. After petrographic characterization, the magnetic properties of the individual grain can be determined by the use of vibrating sample and small-reentrant cryogenic magnetometers, an A.F. demagnetization unit, and a sensitive Curie balance system.

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