Anthracite (Gr. like coals, from coal), the most condensed variety of mineral coal, containing the largest proportion of carbon and the smallest quantity of volatile matter. Excepting the diamond, anthracite is the purest form of carbon in its natural state. The best specimens contain 95 per cent. carbon, but the average production of the purest beds of this coal will not exceed 90 per cent., and generally not more than 80 to 87 per cent. carbon. The volatile matter in the dense, hard varieties is almost exclusively water and earthy impurities, but in common varieties the volatile portion consists of water, hydrogen, oxygen, and nitrogen; while the ash or incombustible matter contains oxide of iron, iron pyrites, silica, alumina, magnesia, lime, etc. The gradation of anthracite is arbitrary; there is no fixed limit in the descending scale at which anthracite becomes semi-anthracite. A coal containing 80 per cent. carbon may be and often is termed anthracite, while other coals containing 80 per cent. carbon are truly semi-bituminous. The superior density, irregular fracture, and general appearance of anthracite are distinguishing features to common observation; while water and ash take the place of hydrogen and oxygen, or bituminous matter.
But anthracite which contains only 80 per cent. carbon, with 20 per cent. water and incombustible matter, is the lowest grade of commercial coal, and of little value as fuel. - The constituents of anthracite, as determined by ordinary analyses, and generally published, are only approximate.