Combining universal-stage, backscatter electron imaging and electron backscatter diffraction for improved indexing of planar microstructures in quartz and plagioclase

Quartz and feldspar commonly develop planar microstructures due to shock metamorphism. These are generally investigated and indexed (identifying the crystallographic orientation along which they developed) using a universal stage (U-stage) on a petrographic microscope. However, the U-stage method alone can sometimes prove insufficient for correct indexing, for example, due to the size of microstructural features, or challenging, in the case of low symmetry minerals. Neither backscatter electron (BSE) imaging nor electron backscatter diffraction (EBSD) analysis can solve this problem individually for a flat surface, as both methods are limited to providing 2-D microstructural information. We propose a method combining contributions from U-stage, BSE imaging and EBSD. The combination and plotting of crystallographic orientation (from EBSD), U-stage measurements of planes and directions, and traces of planar microstructures (from BSE images) in a single reference frame allows the identification of the most probable orientations of features that could not be indexed by applying any single technique. The applicability and limitations of the proposed method were tested on selected shocked quartz and feldspar grains. The method proved to be successful and could be applied to study any 3-D planar features suspected to be aligned with crystallographic planes of an optically transparent host material.