Chapter 10: Petrofabric Analysis by Means of the X-Ray Diffractometer*
The sample holder designed for adaptation of a Norelco X-ray diffractometer to petrofabric analysis permits relatively rapid definition of preferred crystallographic orientations. A complete diagram is obtained in about 3 hours by examination of one sample. Moreover, diagrams are obtained by plotting directly the intensities recorded on a strip chart. Absorption and geometric corrections are unnecessary because, by studying hemispherical surfaces, absorption is held constant, and, by construction of the sample holder, misalignment problems are eliminated.
Three rocks—Poughquag quartzite, Yule marble, and Solenhofen limestone—were studied. Orientations in the quartzite and marble determined by X rays are in excellent agreement with fabrics obtained from microscopic measurements. The quartzite exhibits a preferred a axis as well as a c v orientation. X-ray diagrams record changes in crystallographic orientations for experimentally deformed Yule marble. The limestone, which is too fine-grained to be studied optically, exhibits a slight tendency for preferential c v orientation.