Transmission electron microscopy accompanied by energy-dispersive spectroscopy and selected area electron diffraction of density-gradient separates from two lithotypes of the low-ash, low-sulfur Blue Gem coal, eastern Kentucky, revealed an array of previously unrecognized (in this coal, and arguable in most others) sub-micron minerals, some < 10 nm in size. The sample representing the 1.22-1.24 specific gravity fraction of the middle bench contains a mineral identified as a La-, Ce-, Nei-bearing monazite; other minerals with Cr-Fe, Cu-Fe-S, Fe-Zn-S, and Pb; and areas, probably comprising agglomerates of several grains, if not several minerals, with concentrations of Mg, Ca, Ti, Fe, Zn, Zr, and Mo. The sample representing the 1.30-1.31 specific gravity fraction of the basal lithotype has aggregates of particles enriched in Mg, Ca, Ti, and Fe. Individual grains not specifically quantified include Cr-Ni-Mn-Cu-Fe-S, Ag-S, and Cu-S. Detailed investigation of one area (most of the variation within a < 4 mu m(2) region) demonstrates the presence of greenockite (CdS); minute phases containing Ni-Co-Ge and Ag-Cd-Bi, the latter with a more evident S association than the former; metallic Bi; nisnite (Ni3Sn); silver cadmium; manganosite (MnO); and siderite. Some minerals, such as the monazite, are most likely of detrital or tuffaceous origin. Many of the other assemblages could be of hydrothermal origin, a hypothesis supported by known regional geochemical and coal rank trends, but not previously demonstrated in mineral assemblages at the 10's of nm scale in this region.