In situ and detrital chrome spinels from the Rum layered intrusion, Scotlan
d, show a wide compositional range, In situ, within-seam spinels are relati
vely rich in Al and Mg, and poor in Ti, Cr, and total Fe, In contrast, detr
ital spinels have high Cr, total Fe, and Ti contents and low Al and Mg cont
ents and were derived from spinels disseminated throughout the complex. Our
data show that the widely used petrogenetic discrimination diagrams are no
t based on representative data and cannot, therefore, be applied in either
provenance studies or the interpretation of altered ophiolitic bodies.