The reflectance of a coal sample is usually measured on the vitrinite macerals because this group of macerals shows a fairly uniform increase of reflectance with increasing rank. However, there are some important jumps or discontinuities with the increase in rank, especially in the reflectance ranges of 0.6-0.7 (the first coalification jump of Teichmuller, 1970) and 1.30-1.40 (the second coalification jump of Teichmuller, 1970). For example, when the dry, ash-free volatile matter is plotted against the reflectance for a series of coals, discontinuities appear at both of these points. Also the color of spores in transmitted light go from a bright yellow to a dull brown to black (opaque) in this reflectance range. The fluorescence intensity of the various liptinite macerals is high at the lower end and decreases toward the second jump. The fluorescence colors also change from bright yellows and oranges to dull reds and browns. Of course, the biggest change of the liptinite macerals with rank is their disappearance at the second jump. In general, there are no liptinite macerals in coals with a reflectance of greater than 1.4%.
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Principles and Applications Of Coal Petrology
It is the intent of this course to deal with the very broad aspects of coal petrology. In the process of doing this, the authors intend to point out many of the areas in which the science has been applied to geological and various production problems and also to suggest some areas where future work may be of value. The emphasis is to provide some basic reference materials, some procedural techniques and possibly some ideas for those of you who wish to pursue work in this area. This course is not intended to train you as a coal petrologist but rather to give you some ideas of what the capabilities and limitations of the field are, and to help you get started on your own if you wish to pursue any of these ideas to greater length.