Petrographic examination of sedimentary rocks in the SEM using backscattered electron detectors

Most of the geological work in scanning electron microscopy has been undertaken using the secondary electron (SE) mode and, to a lesser extent, the cathodoluminescence (CL) mode, but in the last few years attention has been drawn to the advantages of imaging with backscattered electrons (BSE). The coefficient of electron backscattering from polished specimens is strongly dependent on average atomic number, allowing different mineral phases to be distinguished on the basis of differences in gray level. A great deal of useful information about the size, distribution, shape, orientation, and textural relationships of minerals in situ can be gained from BSE images. These data can be processed by various image-analysis systems which are now commercially available. This paper reviews the nature and formation of BSE electrons, discusses some of the problems which limit the quality of BSE images of sedimentary rocks, and illustrates some applications of the technique.