Anisotropy of Vitrinite Reflection for Coal and Anthracite

Research on the anisotropy of vitrinite reflection for coal is reviewed, and the criteria for assigning vitrinite to a specific optical type are determined. The available categories are as follows: uniaxial negative, uniaxial positive, biaxial negative, biaxial positive, and biaxial even. Clear assignment of vitrinite to a specific type is possible thanks to Kilby’s method (1988, 1991): that is, the determination of three primary reflectance indicating surface (RIS) axes (Ro, MAX, Ro, INT, Ro, MIN) in disoriented vitrinite grains of coal after standard crushing, as well as the standard RIS parameters: Rst, Ram, and Rev. On the basis of Kilby’s method, in combination with geological factors on coalification, it is possible to identify distinctive features in the RIS character of coal and anthracite, at room temperature or after heating. The present work addresses this topic for Russian coal, which has not previously been studied by this means. Kilby’s method is used to investigate the anisotropy of vitrinite reflection for some Kuznetsk Basin coal samples. In addition, the RIS strain ε of the coal samples is compared by Wei’s method (2017).