A study of the growth sector boundary between the -<i>X</i>and<i>Z</i>sectors in synthetic quartz I. Direct image contrast

Abstract

Abstract The results of an analysis of the crystal deformation and X-ray topographical evidence in support of a previously proposed model of the -X/Z growth sector boundary in synthetic quartz (Parpia 1976) are presented in greater detail. It is shown that the interface between the growth sectors, which have differences in their unit cell dimensions, is coherent. From the analysis of the lattice deformation in a simple two-sector bar it is predicted, using linear elasticity theory, that the direct image will generally form on Lang topographs near the boundary outcrops. In the interior region of the specimen, direct image formation will occur only under certain specified conditions. The direct image of the growth sector boundary is predicted to suffer extinction when diffraction is from the lattice planes lying normal to the boundary. The form of the direct image and its extinction effects are observed to be satisfactorily accounted for by the model. The direct image of the growth sector boundary has also been studied by section topography, which further substantiated the proposed model. This latter work confirmed that there was no lamella of material contained at the boundary having unit cell dimensions that were appreciably different to those in the adjacent sectors. Suggestions are made to account for the presence of the bulk strains in the bars of quartz, which, if proven to be correct, could lead to the establishment of new investigative methods to determine the temperatures and/or pressures at which the crystals were grown.