Coal Petrology
The individual organic components of coal are termed “macerals,” similar to “minerals” in rock. Macerals are divided into three broad groups: vitrinite, inertinite, and liptinite. Vitrinites are the coalified remains of humic plant substances, primarily lignin and cellulose. In most cases, inertinites consist of the same original plant material as vitrinite but have been altered by charring or oxidation prior to coalification. Inertinites can also include fungal bodies. Liptinites are the remains of hydrogen-rich plant materials such as cutins, resins, fats, waxes, and sporopollenin (the outer cell walls of spores and pollen). The maceral content of coal is determined with a reflected light microscope (light is reflected from the sample towards the analyst) at magnifications of about 500x, using tungsten filament and gas arc light sources.
Photomicrograph of a coal sample showing the fluorescent liptinite maceral resinite filling cell lumens in woody tissue. The coal sample is from the Wilcox Group (Paleocene-Eocene) in the subsurface of northern Louisiana.
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U.S. Department of the Interior |
U.S. Geological Survey
