Statistical summaries of proximate and ultimate analyses, heat of combustion, and content of 36 major, minor, and trace elements were calculated for 37 Eocene, 470 Paleocene, and 419 Cretaceous coal samples from 31 coal fields or areas in the Rocky Mountain and Northern Great Plains coal provinces and for 503 Pennsylvanian coal samples from 14 areas in the Interior coal province. These analyses show that coals within an age group have similar ranges in composition, and that each group has its own distinctive compositional characteristics. Most variability in element content can be related to changes in rank and differences in ash and total sulfur contents. Mean contents of Ca, Mg, Na, Ba, and Sr are related to rank and decrease as apparent coal rank increases from lignite A to high-volatile B bituminous coal. Mean contents of Si, Al, K, Ti, Ga, Li, Sc, Th, V, Y, and Yb increase as the mean ash content increases (correlation coefficients 0.6), suggesting that these elements are present as aluminosilicates, stable oxides, or phosphate mineral phases. Mean contents of Fe, As, Cd, Co, Cu, Mo, Ni, Pb, Sb, and Zn show high correlation with total sulfur. Contents of these elements are low in Paleocene (0.6% sulfur) and Cretaceous (0.7% sulfur) coals, higher in Eocene (1.8% sulfur) coals, and generally highest in Pennsylvanian (3.9% sulfur) coals. The mean contents of B, Be, Cr, F, Hg, Mn, Nb, Se, U and Zr show no direct relationships to changes in rank or ash and total sulfur contents. Decrease in element content with increased rank probably is related to loss of functional groups that act as cation-exchange sites on organic matter. Ash and sulfur contents are dependent on pH-controlled levels of bacterial activity in ancestral peat swamps.

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