Abstract
Two dimensional lattice defects in KCl crystal were observed by means of optical and X-ray topographic methods. The defects produced three types of the diffraction images on X-ray topographs, that were the symmetric and asymmetric ones for ± g of reciprocal lattice vectors, and the diffuse images for any g . From the appear-disappear relation for various g and the geometrical consideration, it was concluded that the defects are stacking faults, and the fault vector is nearly a /6 which is anti-parallel to the Burgers vector of Shockley partial dislocation in fcc structure, and that the stacking fault is accompanied with an expansion distortion perpendicular to the {111} fault plane. The defects giving asymmetric or diffuse images are concluded to be formed by the superposition of simple stacking faults.