Physical constitution of Illinois coal and its significance in regard to utilization

Eight major minerals were identified in selected Illinois coals in addition to petrographic characterization of the coals. Physical and mineralogical composition was determined utilizing optical microscopy. Extraneous mineral matter (primarily secondary) occurred chiefly as marcasite or pyrite, kaolinite, and calcite. Kaolinite was concentrated in vitrain, while pyrite was the predominant mineral in fusain. Detrital clay, secondary calcite, disseminated pyrite, and kaolinite all commonly occurred in clarain. Sulfate S was found in gypsum in Illinois coals, although only in trace amounts. Primary minerals identified included quartz, feldspar, garnet, and zircon. High kaolinite concentrations were generally accompanied by corresponding low concentrations of pyrite.