Gypsum plate enhancement of cataclastic fabric in thin section

Individual fine particles in cataclastic zones (gouge) are often extremely difficult to distinguish in thin section in either plane- or cross-polarized light. It is equally difficult, using these techniques, to determine the relationship of fine fragments in gouge zones to one another or to their parent material. Cathodoluminescence can greatly improve such observations, but it too has limitations and requires special equipment. This paper discusses how using a gypsum plate, which causes light retardation, can enhance the interference colors of fine particles in gouge such that they are more clearly distinguishable. In addition, if cataclastic deformation within the gouge is not extreme, flow paths and origins for fine particles can be observed by using the gypsum plate, thus providing an easily available, inexpensive tool for the structural petrologist studying finely comminuted material.