Vitrinites, coalification

Pressure of the overburden does not cause chemical reactions which lead to a higher rank. Experiments have shown that static pressure even retards coalification processes. By contrast, pressure affects the physical properties, notably the porosity and moisture content in low rank coals. Further, the optical anisotropy of vitrinites (which is a tension anisotropy) is caused by pressure. Shearing movements have influenced the chemical coalification only occasionally and locally in the foredeeps that we have studied (for instance in the immediate vicinity of overthrusts). In such cases the tectonic movements probably were so quick that the friction heat and the shearing could operate. Shearing in no way can account for the gradual increase in coal rank with depth. 

Extended discussion of these speculative relationships is unwarranted until more critical information is available. The multilinear aspect of coalifi-cation described previously (3, 6) appears to be well illustrated by the Brandon woods. It seems evident that from a single plant tissue various dissimilar materials may result as products of coalification. Those described represent macerals related to the vitrinite, micrinite, and resinite maceral series. Because of the position of these materials in their respective series—i.e., only slightly metamorphosed and anatomically relatable to the woods of extant plants— their detailed study using appropriate chemical and physical methods should reveal useful information concerning the basic composition of coals of both higher and lower rank and simultaneously add to our knowledge of the coalification process. 

In Fig. 87 a coalification band F for vitrinites is also represented. From the straight H O... 

Relationships Between the Organic Structure of Vitrinite and Selected Parameters of Coalification as Indicated by Fourier Transform IR Spectra... 

Some chamical and optical parameters of coalification are reported in Table I for the vitrinite concentrates. Total vitrinite content is included as an indication of sample purity. 

Statistical analyses were performed on FTIR data from the aliphatic and aromatic regions and selected parameters of coalification for 24 vitrinite concentrates from the Lower Kittanning seam. 

ESR of Different Rank Vitrinites. The vitrinite samples provide the opportunity to study the systematics of radical chemistry as a function of the extent of coalification. Perhaps the most striking first observation is that the type of radical is different in subbituminous coals than it is for bituminous coals (with some intermediate behavior for high volatile C vitri-... 

Coal is an inhomogeneous rock, because different types of plant material behave differently under coalification conditions, and mineral matter is not uniformly distributed, either by type or by amount. Microscopic examination reveals this inhomogeneity by showing that different areas of the coal structure have a different appearance. The organic components of coal are classified into six macerals vitrinite, exinite, resinite, semifusinite, micri-nite, and fusinite. The first three of these macerals are reactive (relatively easily hydrogenated or oxidized), and the other three are relatively inert. Most coals are banded,... 

Hatcher P. G., Wenzel K. A., and Cody G. D. (1994) The coalification reactions of vitrinite derived from coalified wood transformations to the rank of bituminous coal. In Vitrinite Reflections as a Maturity Parameter (eds. P. K. Mukhopadhyay and W. G. Dow). American Chemical Society, Washington, DC, pp. 112-135. 

McCartney J. T. and Teichmuller M. (1972) Classification of coals according to degree of coalification by reflectance of the vitrinite component. Fuel 51, 64—68. 

Because of the complexity of the coalification processes, different measures are used to define different levels of rank (Table I) high moisture, low heating value, and nonagglomerating character of the coal define the rank (group) within the lignite and subbituminous classes and volatile matter (or fixed carbon) define the various groups of rank in the bituminous and anthracite classes. In addition to these properties, the reflectance of vitrinite, carbon content of the coal (dry, mineral matter free), and some other properties change proportionately as rank increases (Table I). 

Smith, G.C. and Cook, A.C. 1980. Coalification paths of exinite, vitrinite and inertinite. Fuel, 59 641. 

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