In situ and detrital chrome spinels from the Rum layered intrusion, Scotland, show a wide compositional range. In situ, within-seam spinels are relatively rich in Al and Mg, and poor in Ti, Cr, and total Fe. In contrast, detrital spinels have high Cr, total Fe, and Ti contents and low Al and Mg contents and were derived from spinels disseminated throughout the complex. Our data show that the widely used petrogenetic discrimination diagrams are not based on representative data and cannot, therefore, be applied in either provenance studies or the interpretation of altered ophiolitic bodies.

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