Mineral Matter in Illinois and Other U.S. Coals

This review (1) describes and classifies the geological, physical, and chemical occurrences of mineral matters in coal; (2) summarizes analytical methods used to characterize the mineral matter; and (3) compares the mineral-matter composition of Illinois coals with that of other U.S. coals. In Illinois coals the organic constituents generally vary vertically within seams by a factor of 2 to 3; many elements also vary laterally within the same seam. Similarly, variations are substantial from one seam to another within the Illinois Basin. There is a considerable overlap, however, in compositional ranges of coals from different U.S. basins. On a regional basis, the material variability of many elements, such as sulfur and chlorine, is the result of geological processes. Low-sulfur coals mined in many western states, southern West Virginia, southwestern Virginia, and eastern Kentucky underlie strata deposited from fresh water; whereas many high-sulfur seams underlie strata deposited from sulfate-bearing brackish or marine waters. Because of the high variability of coal, samples from all prospective deposits need to be analyzed. Methods for analysis of inorganic elements in coal are generally precise, but methods for quantitative analysis of mineral phases need to be improved.