On the multiple orientation relationships between hematite and magnetite

Lattice fringe and diffraction observations of hematite/ magnetite interfaces are described: elongated laths of magnetite, with (111)M and ({ 1}11)M parallel to (0001)H and, less frequently, (211)M and ({ 2}11)M parallel to (0001)H, were found. In general, the interfaces are incoherent as shown by the presence of steps, which are probably transformation dislocations. The magnetite is invariably multiply twinned, showing steps which may be twinning dislocations. A theoretical analysis of the possible secondary and ternary orientation relationships due to multiple twinning explains one of the two further less-frequent relationships indicated by texture goniometry. Such higher-order relations are not topotaxic and their identification and interpretation is a general problem for texture goniometry.