X‐ray Topographic Study of Defects in Quartz I. Brazil Twin Boundaries

Abstract

Abstract A systematic investigation has been made of the diffraction contrast effects observed by X‐ray traverse topography at Brazil twin boundaries in natural quartz. Evidence is presented to show that the crystal axes are not coincident across the Brazil twin boundaries but are displaced by a vector R which depends upon the composition plane of the boundaries. Consequently the displacement vectors for intersecting Brazil twin boundaries are not identical. These displacement vectors have been determined from the observed vanishing conditions for the diffraction contrast fringes at the boundaries. The expected stair‐rod type dislocations at the intersections of the twin boundaries have been found. Probable atomic models for the Brazil twin boundaries are proposed and discussed.