An X-ray method for studying orientation of micaceous minerals in shales, clays, and similar materials

Abstract

Micaceous minerals, such as the micas, the chlorites, and most clay minerals, usually develop as thin lamellae parallel to the crystallographic basal plane (001). In sedimentary deposits these lamellae tend to lie parallel to the bedding plane and in slates parallel to the cleavage. Their degree of orientation is likely to vary with the conditions of formation of the material, and in the case of slates Bates (1947) has shown that it is closely related to their fissility. In relatively coarse-grained materials the degree of orientation may be studied directly by suitable microscopic techniques, but with fine-grained materials X-ray methods must be used, and even with coarser-grained materials the use of X-ray methods may have advantages, especially if a scanning technique, such as that described by Thewlis and Pollock (1950), is employed.