Higher-order structural relationships between hematite and magnetite

Matrix-transformation techniques are developed to describe the numerous higher-order orientation relationships possible between hematite and magnetite when multiple twinning of both phases is allowed. Structural models for the various interfaces are described. The matrices are used to predict the peak positions expected for the 400_M pole figure of magnetite on hematite. Comparison with the experimental pole figure [Becker, Heizmann & Baro (1977). J. Appl. Cryst. 10, 77-78] showed that it was also necessary to allow for oriented recrystallization of hematite. This involves a new distinct type of orientation relationship which is labelled transformation twinning.