Figure F46. Magnetic mineralogy observed in four thin sections. A. Fine opaque particles in siltstone containing unidentified ferrimagnetic grains and organic fragments. Green mineral left of center is glauconite. B. Framboidal iron sulfate magnetic minerals (upper center right) formed in a pore possibly carrying a secondary magnetization. C. Series of fine magnetic minerals situated along glauconite pellets show an authigenic origin. D. Subangular magnetite grain (center, opaque) showing detrital origin.
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