SUBBITUMINOUS COAL

also called Black Lignite, dark brown to black coal intermediate in rank between lignite and bituminous coal. Subbituminous coals often have a silky lustre and sometimes are macroscopically indistinguishable from the bituminous variety. The fibrous structure characteristic of lignite is absent in subbituminous coals, many of which have evolved alternating dull and bright bands similar to those of bituminous coals. Subbituminous coals are much harder than lignites. Although subbituminous coals have relatively low heat value, their sulfur content is lowoften less than 1 percent. For this reason, an increasing number of coal-fueled electric-power plants in the United States have turned from bituminous coals to subbituminous coals and lignites, which also have a low sulfur content. See also bituminous coal; lignite.