[1] Magneto-optical imaging based on the Faraday effect has been used
to characterize magnetic minerals embedded in a nonmagnetic matrix. We
have studied magnetite grains and magnetite-magnetite grain boundary
regions in samples of skarns and serpentinites. Distributions of the
remanent magnetic field were measured across at the surface of polished
thin sections kept at room temperature. The magneto-optical images
resolve directly magnetic structures on length scales ranging from
millimeter down to micrometer, thereby revealing the shape and
arrangement of the magnetite grains and allow determination of the grain
magnetization. We find that ( 1) for the skarns the intergrain
interactions do not affect the magnetic properties of magnetite grains
within 0.6 - 60 mu m of each other, while the saturation remanence
decreases weakly with increasing grain size from 40 mm to 0.6 mm, and (
2) for the serpentinites the magnetic properties of the stripes are
size-dependent due to variations in chemical composition.