A cathodoluminescent study of quartz sand grains

Abstract

SUMMARYSurfaces and cross sections of individual quartz sand grains have been examined in both the emissive and cathodoluminescent (CL) modes using a scanning electron microscope. The cathodoluminescent micrographs reveal sub‐surface information not seen in the emissive mode micrographs. The CL features are generally associated with previous stressing, fracturing or abrasion of the grains, and are probably related to the formation of disrupted‐lattice and/or amorphous quartz. The sequence of events during the formation of these features can be identified on many grains by studying the spatial distribution of the most common form of CL contrast—narrow dark bands. On other grains, irregularly distributed dark patches are generally observed to be a surface phenomenon, but the distribution, depth and intensity of these features can be studied by examining cross sections of grains. While it is common for the banded features to cross the entire specimen, it is rare for the diffuse areas to penetrate more than 30 μm. Some grains when experimentally heated above the α‐β transition temperature show a marked change and even a complete reversal in CL contrast.Such studies of grains in cathodoluminescence can supplement the environmental information obtained from emissive mode micrographs of geological materials.