Macerals, classification

A number of subdivisions of the maceral groups have been developed and documented by the International Commission on Coal Petrology (14). Table 1 Usts the Stopes-Heeden classification of higher rank coals. Periodic revisions include descriptions of the macerals, submacerals, morphology, physical properties, and chemical characteristics. Theories on the mode of formation of the macerals and their significance in commercial appUcations are also included of Reference 14. 

Table 1. Stopes-Heerlen Classification of Maceral Groups, Macerals, and Submacerals of Higher Rank Coals ...

The macerals in lower rank coals, eg, lignite and subbiturninous coal, are more complex and have been given a special classification. The term huminite has been appUed to the macerals derived from the humification of lignocellulosic tissues. Huminite is the precursor to the vitrinite observed in... 

This classification of the seams is justified and is well reflected in the proximate analyses and distribution of the vitrinoid types distinguished on the basis of reflectance values. The variation of the different macerals in each zone is shown in Figures 4 and 4a. 

Coal lithotypes are megascopically recognizable components of coal. Several nomenclatures have been used to identify the lithotypes [see Damberger et al. (54) for a review of several common classifications]. Coal lithotypes have fairly distinct maceral compositions, which originate from different combinations of plant materials and evolve along somewhat different paths during coalification. 

As unifying, underlying concepts, type and rank certainly can be employed to envision why coals have the properties that they do. However, it is time for a reevaluation of coal classification concepts. How can we measure rank when we analyze coals of different types and when there is no simple rank progression even when vitrinite or vitrinite-rich coals are compared And how can we assess type when maceral identification criteria are highly subjective, except for reflectance measurements that routinely are not even applied to the liptinite and highly variable inerti-nite macerals And, finally, how can coals be classified scientifically when empirical and derived properties like calorific value and fixed carbon yield are employed as classifying parameters ... 

This classification is useful in that the removal of minerals from coal in preparation plants is strongly influenced by the mineral s physical mode of occurrence. Fine-grained quartz, clay, and pyrite disseminated within macerals are least susceptible to removal by physical cleaning methods whereas rock fragments and minerals in layered, nodular, and fissure modes break free and are more easily removed. 

Suarez-Ruiz and Crelling, 2008). Indeed, it would be most surprising if this were not the case in view of the differences in ultimate composition alone of the various macerals (Table 4.10). Furthermore, it appears that no two coals (no matter how close their relationship is in the various classification systems) have exactly the same petrographic composition and, consequently, the... 

In addition to rank, two other parameters are important in coal classification, type and grade. Type of coal refers to the amount and sort of organic constituents called macerals (see below), whereas grade refers to the relative purity or the amounts of ashforming minerals found in coal. 

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