The mineralogy of coal ash is systematically distributed in recognizable patterns which are in turn a response to the basic depositional and early diagenetic geologic processes of the area. In general, the main control over the basic mineralogy of the ash appears to be the relative influence of the marine environment of the coal-forming swamp. Systematic changes in ash composition can be observed as one proceeds eastward from the Mid-Continent Coal Basin through the Illinois and Dunkard Basins to the Pocahontas Basin of southern West Virginia as the coal-forming environment becomes less influenced by marine conditions. The fresh-water coals of the western fields have ash compositions which compare closely with the lower Pottsville coals of the Pocahontas Basin. Systematic variability also exists on a within-a-mine basis where non-random patterns of sulfur and ash appear to reflect both de-positional and post-depositional processes.