Summary: The parageneses of opaque minerals in three Assynt rocks are described. A biotite-diorite dyke-rock of Lewisian age is characterized by a primary igneous assemblage of Fe-Ti oxides, pyrrhotine, and pentlandite. Effects of metamorphism are recognized, particularly in the oxidation of ilmenite in a Lewisian epidiorite dyke-rock. Cromaltite contains a primary assemblage of oxide minerals together with a later hydrothermal sulphide assemblage. Evidence from the opaque minerals cannot be reconciled with a theory of limestone assimilation. The correlation of the distribution of Co, Ni, and Cu in the rocks with the opaque minerals present is considered.