Current uses of fluorescence microscopy in coal petrology

Abstract

SUMMARY Fluorescence analysis of the liptinite maceral content of various U.S. coal seams has shown that these macerals are consistently under‐counted in conventional white‐light analysis. Fluorescence analysis revealed a greater variety of liptinite macerals as well as a large amount of fluorescing vitrinite in all of the coals studied. However, pseudovitrinite was not observed to fluoresce. Textures and structures not visible in normal viewing are also seen in fluorescence analysis. Quantitative spectral analysis of single coals has shown that most liptinite macerals can be both petrographically and statistically separated on the basis of fluorescence parameters, with the wavelength at maximum intensity and the red/green quotient being the most significant. In coals of the Illinois Basin, one or more forms of fluorinite, resinite, sporinite and cutinite can be distinguished. As the rank of the coal increases, the fluorescence intensity decreases and the spectral maxima shift toward longer wavelengths. In some Rocky Mountain coals these effects occur at a much lower rank (<0.85% reflectance) than in the coals of the Appalachian Basin. Similar changes in fluorescence properties have also been found in naturally weathered coals. Fluorescence analysis of resinite‐rich Rocky Mountain coals has shown that two major forms of resinite are present; one is the ‘normal’ resinite, and the other is a much more abundant fissure‐filling resinite that carries coal xenoliths, shows flow structure, and has a spectral maximum well below that of the ‘normal’ resinite.