Diffraction Contrast from Dauphiné Twin Boundaries in Quartz

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Abstract
Electron diffraction contrast evidence is obtained for the presence of Dauphiné twins in amethyst quartz. A model for the Dauphiné twin boundary which does not involve broken SiO bonds is proposed and shown to be consistent with the contrast features observed with different operating reflection. X‐ray diffraction topography of macroscopic Dauphiné twin boundaries in natural quartz show identical contrast effects and support the electron microscope observations. – It is shown that a different type of fringe pattern, not previously described, can arise at boundaries if the extinction distances in the two parts of the twin differ significantly. Diffraction contrast from such fringe patterns is described and explained using Gevers‐Amelinckx intensity relations.