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Summary
COAL IS CONSIDERED TO BE COMPOSED OF TWO PRINCIPAL PARTS, an organic part and an inorganic part. The microcomponents and microstructures that make up the organic part are called macerals, which are considered to be the building blocks of coal, in the same way minerals are the building blocks of rocks. There are three principal types of macerals, which are optically discrete particles of organic material in coal. Inertinite is maceral material derived from the partial carbonization of the coal-forming materials by fire or intensive degradation by microorganisms. Vitrinite is derived from woody tissues and is the most abundant maceral in coal. Exinite, also known as liptinite, is derived from spores, needles and leaf cuticles, plant resins, and similar materials. Table 5 lists some examples of petrographic values for coals of different ranks. The data in Table 6 illustrate the relative amounts of carbon, hydrogen, and oxygen present in the different types of macerals. The amounts of these three elements illustrate the relative reactivity of the various types of macerals. The percentages of volatile matter, which is a measure of the mass loss of the coal when heated to 950 C in an inert atmosphere, that are listed for the macerals are an indication of the relative reactivity of the various types of macerals, or that exinite macerals are much more reactive than inertinite macerals. The aromaticity of the maceral groups is the ratio of the aromatic hydrocarbon character to the aliphatic hydrocarbon character in the organic materials. The aromaticities of the maceral groups are also indications of their relative reactivities, with macerals having lower aromaticities being more reactive.
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Electronic reproduction. W. Conshohocken, Pa. : ASTM International, 2007. Mode of access: World Wide Web. System requirements: Web browser. Access may be restricted to users at subscribing institutions.
