Figure 13. Photograph and photomicrographs of Pennsylvanian bituminous coal. A, Photograph of a lump of bituminous coal from Pennsylvania showing typical banding caused by layering of a variety of preserved plant types as they accumulated in an ancestral peat swamp. Magnification ×0.55. B, Photomicrograph of a thin section of a small piece of bituminous coal from Illinois photographed in transmitted light. Magnification approximately ×330. C, Photomicrograph of a polished surface of a small piece of bituminous coal from Pennsylvania photographed in reflected light. Magnification approximately ×250. Parts B and C show some typical constituents—macerals (plant remains) and minerals—found in bituminous coals. Macerals are abbreviated as follows: V, vitrinite; F, fusinite; S, sporinite; and R, resinite. Minerals are abbreviated as follows: P, pyrite; and C, clay-sized minerals. The scale bar on parts B and C is 50 micrometers, which is equivalent to about 0.002 inch. The lump of bituminous coal is included to provide a comparison between what can be seen in a lump of coal and the wealth of detail in coal that can be seen with high magnification. The lump of coal is approximately 260 times larger than the chips of coal represented by either of the photomicrographs. Photographs and photomicrographs by R.W. Stanton (U.S. Geological Survey).