X-ray Diffraction by a Layer Silicate containing Stacking Faults

Abstract

IN cronstedtite, as in many layer-type silicates, structural faults occur during the growth of the crystals which consist of displacements of the layers from their correct positions. Since the direction of the displacements is parallel to the layers, their effect is to destroy the regularity of the structure in the direction perpendicular to the layers, considered here to be the direction of the c*-axis of the reciprocal lattice, and the reciprocal lattice points become smeared along this axis. On an X-ray diffraction photograph, spots on a row of constant h and k and varying l are linked by a streak which varies in intensity from a maximum at the positions of the spots to a lower value between them. The extent of the streaking depends on the frequency of the faults, and varies from one crystal to another.