X-Ray Analysis of Preferred Orientation in Fine-Grained Quartz Aggregates

Abstract

The preferred orientations of quartz in a number of small fine-grained specimens of experimentally deformed and recrystallized flint were determined with a Norelco pole figure goniometer. The device was modified by introducing small (0.5-1.0 mm.) collimators to examine restricted areas of flat specimens in both the reflection and transmission modes. Scans in the two modes were combined to yield complete pole figures. The preferred orientations in the specimens are shown to be axially symmetric and are given by intensity profiles extending 0°-90° from the symmetry axis. Profiles for as many as fifteen diffraction peaks from individual specimens are subjected to spherical harmonic analysis to obtain a complete determination of the preferred orientation (the crystallite distribution function), which is represented concisely in the form of an inverse pole figure. From the inverse pole figure the preferred orientation of any crystallographic direction (such as the [0001] direction in quartz, which is difficult to measure directly) may be generated. Similarly, the preferred orientations of positive and negative trapezohedral and rhombohedral forms (such as the pairs , respectively), which cannot be resolved by standard X-ray measurements, are separately determined. Earlier work with polymers and metals using these methods is reviewed. The methods are illustrated by means of two flint cylinders recrystallized during compression at high temperature and pressure; one (GB-3) is relatively homogeneous and the other (GB-11) shows marked variation in preferred orientation. There are differences in the orientations of the positive and negative forms in both specimens. The preferred orientations may be characterized as a mixture of two components: (a) parallelismof c = 0001 with the compression axis and (b) parallelism of the poles of the positive unit rhomb with the compression axis. The latter component dominates in the more coarsely recrystallized (hotter) regions of specimen GB-11.