Reflectance maceral composition

Petrographic continuity of layers may reflect widespread simultaneous deposition of a given maceral composition. If this is true, it is probable that physical and chemical aspects of the peat swamp are more significant factors than local florisbc similarities in establishing the organic composition of the layer. 

The studies carried out consist of the megascopic description of the master columns study of thin sections for maceral assessment, determination of maceral composition on polished blocks in reflected light, determination of mean maximum reflectance values on polished pellets, proximate analyses of selected petrographic zones, hot stage studies on vitrinoids to determine the thermal behavior at various temperatures, electron microprobe and spectrochemical studies of selected zones to determine the nature of ash forming elements, analyses of certain zones petrographically important to determine the variation of total carbon, and hydrogen and microhardness determinations on certain macerals. 

Coal reflectance (ASTM D-2798) is very useful because it indicates several important properties of coal, including determination of the maceral composition of coal, which, in turn, is helpful for the prediction of behavior in processing (Davis, 1978 Davis et al., 1991). Coal reflectance is determined by the relative degree to which a beam of polarized light is reflected from a polished coal surface that has been prepared according to a standard procedure (ASTM D-2797). Samples prepared by this practice are used for microscopical determination of the reflectance of the organic components in a polished specimen of coal (ASTM D-2798) as well as the volume percent of physical components of coal (ASTM D-2799). 

Liptinites generally make up about 5%-15% of most North American coals. They are usually more abundant in the Appalachian coals than any other US coals except cannel and boghead types where they dominate. At a reflectance of 1.35-1.40, most of the liptinite macerals disappear from coal. Cannel and boghead coals are petrographically distinguished from humic coals by both their maceral composition and texture. They have an abundance of liptinite macerals (sporinite in can-nels and alginite in boghead coal) and a relative low level of vitrinite and inertinite macerals. 

Coal reflectance is important in aiding the determination of the maceral composition of coal which, in turn, is helpful for the prediction of behavior in processing (Davis et al., 1991) (Chapter 4). For example,... 

On the microscopic level, the lithotypes just described are seen to be composites made up of discrete entities called macerals. Optically differentiated by microscopic examination of coals under reflected light or by the study of thin sections of coal using transmitted light (Fig. 1), macerals are classified into three major groups vitrinite. 

The properties of coal are affected by the composition of the coal. Furthermore, the natural constituents of coal can be divided into two groups (1) the organic fraction, which can be further subdivided into microscopically identifiable macerals and (2) the inorganic fraction, which is commonly identified as ash subsequent to combustion. The rank (thermal maturity) of the organic fraction of the coal is determined by the burial depth (pressure) and tanperature. The composition of organic (non-mineral) fraction changes with rank with the main indicators of rank bringing the reflectance of the vitrinite, carbon, and volatile matter content on a dry ash-free basis. 

The maceral content defines the coal type sapropelic, with >50% liptinite, or humic, more abundant, usually presenting a banded structure. On the other hand, based on the different optical properties of macerals, the reflectance of vitrinite is an essential characteristic used in coal identification and related to rank. A good analysis of maceral content provides knowledge about the chemical composition of a coal, their behavior in different conversion processes, and can also be used as a parameter of coal rank (see section on Petrographic analysis). 

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