Crystallographic relations between face- and body-centred cubic crystals formed under near-equilibrium conditions: Observations from the Gibeon meteorite

The orientations of the kamacite lamellae formed from a single prior-taenite grain were measured by analysing the electron backscatter diffraction patterns obtained using scanning electron microscopy. These are shown to be close to the Kurdjumov-Sachs and Nishiyama-Wassermann relations and their intermediate, i.e., the Greninger-Troiano relation. The orientations of the α grains in the plessite regions were also measured and these were found to be continuously distributed around the Bain circles formed by the variants of the common correspondence relationships, including the Pitsch one in this case. The local misorientations between individual face- and body-centred cubic crystals along their common interfaces were measured. These can be characterized by the orientation relationships mentioned above as long as a certain amount of tolerance is allowed. Orientation variations within individual kamacite lamellae were also analysed. The crystallographic data support the view that somewhat different mechanisms are involved in the formation of Widmanstätten structures and of the plessite in meteorites.