Two basic intrusions in the Caledonian of western Scotland were studied by optical microscopy, electron microprobe analysis, scanning and transmission electron microscopy, and X-ray diffraction. Ilmenite occurs in 8 orientations (4 pairs in which members of a pair are equivalent by the symmetry of the hornblende). Rutile occurs in 6 orientations (4 symmetrically distinct orientations). The orientations are interpreted in terms of the fully O-rotated model amphibole structure, in which the oxygen atoms are cubic close-packed. It is possible that the ilmenite and rutile were exsolved, in a closed system, from a parental amphibole with a normal structural formula.--Modified journal abstract.

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