Special Research Report SR-118
Geologic stresses during coalification impart on anisotropic re- flectance fabric to coal. This property was used to help interpret finite strain paths, timing and sequence of Alleghenian Orogenic events in Pennsylvania. The reflectance configuration is represented by the Coal Reflectance Indicatrix (CRI), which is biaxial for all coals analyzed. The magnitudes and orientations of the three principal axes (RMAX (maximum), RINT (intermediate), and RMIN (minimum)) were empirically determined by analyzing three nearly orthogonal surfaces taken from oriented sample blocks. The magnitudes alone could be derived from the analysis of nonoriented samples, using a new estimation procedure. This involved the measurement of apparent maximum and apparent minimum reflectances on many randomly-oriented grains of vitrinite. The Flinn a-b diagram was adapted to depict all possible CRI shapes (oblate to prolate), as well as simplified deformation paths.
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