Application of the crystallographic orbit analysis to the study of twinned crystals. The example of marcasite
Abstract
The continuity of a substructure across the interface is considered a necessary condition for the formation of a twin. The application of the analysis of the eigensymmetry of crystallographic orbits to the derivation of this structural continuity is briefly reviewed and applied to the analysis of the \101\ twin in marcasite. This analysis shows that one fourth of the structure, but half of the substructure near the composition surface, is common to the two orientations realized in the twin, the operation mapping the common atoms in the twinned domains being an n-glide occurring every one fourth of the period along the direction quasi-perpendicular to the twin plane. The existence of this significant common substructure justifies and explains the formation of the twin.