Scanning Microscopy


The scanning electron microscope (SEM), equipped with an energy dispersive X-ray analyzer (EDX), has been widely used to study the inorganic geochemistry of coal. This system was instrumental in establishing that the bulk of most trace elements in bituminous coals are associated with fine-grained accessory minerals. Textural evidence, as observed in the SEM, indicates that many of these minerals are embedded in relatively large organic particles. As a consequence of this association, these minerals, and the elements they contain, can be rafted up into the lighter specific gravity fractions during sink-float separation of the coal. Textural evidence also indicates the presence of two distinct mineral suites. The first suite includes kaolinite, sulfides, carbonates, and crandallite-group minerals. They occur predominantly in the pores of the inertinite macerals. These minerals commonly exhibit crystal faces and are intimately intergrown with one another. An authigenic origin is indicated for these minerals. The second suite occurs in bands of intermixed maceral fragments and angular to subrounded mineral grains that are probably of detrital origin. This suite includes quartz (some rutilated), illite, mixed-layer clays, rutile, and zircon.

The perfection of ancillary techniques, such as cathodoluminescence and automated image analyses, will enhance the future value of the SEM in the study of coal geochemistry.

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