Sub-bituminous coal is black; and as it is mined, it looks a great deal like the bituminous coal seen in coal yards. It contains from 15 to 30 percent moisture. The range of heating value of cub-bituminous “A” coal is the same as that of high-volatile “C” bituminous coal. Sub-bituminous coal is entirely non-coking. Like lignite, it weathers or slacks rapidly upon exposure to air and is subject to spontaneous combustion if not stored properly. Because of the same disadvantageous features as lignite, it is used principally in the areas where it is mixed.