Anthracite is a hard, compact variety of coal that has a submetallic luster. It has the highest carbon content, the fewest impurities, and the highest energy density of all types of coal except for graphite.
Anthracite is the most metamorphosed type of coal (but still represents low-grade metamorphism), in which the carbon content is between 92% and 98%. The term is applied to those varieties of coal which do not give off tarry or other hydrocarbon vapours when heated below their point of ignition. Anthracite ignites with difficulty and burns with a short, blue, and smokeless flame.
Anthracite is categorized into standard grade, which is used mainly in power generation, and high grade (HG) and ultra high grade (UHG), the principal uses of which are in the metallurgy sector. Anthracite accounts for about 1% of global coal reserves, and is mined in only a few countries around the world. China accounts for the majority of global production; other producers are Russia, Ukraine, North Korea, South Africa, Vietnam, the UK, Australia, Canada and the US. Total production in 2010 was 670 million tons.
Anthracite is similar in appearance to the mineraloid jet and is sometimes used as a jet imitation.
Anthracite differs from ordinary bituminous coal by its greater hardness (2.75–3 on the Mohs scale), its higher relative density of 1.3–1.4, and luster, which is often semi-metallic with a mildly brown reflection. It contains a high percentage of fixed carbon and a low percentage of volatile matter. It is also free from included soft or fibrous notches and does not soil the fingers when rubbed. Anthracitization is the transformation of bituminous coal into anthracite.
The moisture content of fresh-mined anthracite generally is less than 15 percent. The heat content of anthracite ranges from 22 to 28 million Btu per short ton (26 to 33 MJ/kg) on a moist, mineral-matter-free basis. The heat content of anthracite coal consumed in the United States averages 25 million Btu/ton (29 MJ/kg), on the as-received basis (i.e., containing both inherent moisture and mineral matter). Since the 1980s, anthracite refuse or mine waste has been used for coal power generation in a form of recycling. The practice known as reclamation is being applied to culm piles antedating laws requiring mine owners to restore lands to their approximate original condition.
Chemically, anthracite may be considered as a transition stage between ordinary bituminous coal and graphite, produced by the more or less complete elimination of the volatile constituents of the former, and it is found most abundantly in areas that have been subjected to considerable stresses and pressures, such as the flanks of great mountain ranges. Anthracite is associated with strongly deformed sedimentary rocks that were subjected to higher pressures and temperatures (but short of metamorphic conditions) just as bituminous coal is generally associated with less deformed or flat-lying sedimentary rocks. For example, the compressed layers of anthracite that are deep mined in the folded Ridge and Valley Province of the Appalachian Mountains of the Coal Region of East-central Pennsylvania are extensions of the same layers of bituminous coal that are mined on the generally flat lying and undeformed sedimentary rocks further west on the Allegheny Plateau of Kentucky and West Virginia, Eastern Ohio, and Western Pennsylvania. In the same way the anthracite region of South Wales is confined to the contorted portion west of Swansea and Llanelli, the central and eastern portions producing steam coal, coking coal and domestic house coals.
Structurally, anthracite shows some alteration by the development of secondary divisional planes and fissures so that the original stratification lines are not always easily seen. The thermal conductivity is also higher; a lump of anthracite feels perceptibly colder when held in the warm hand than a similar lump of bituminous coal at the same temperature. The chemical composition of some typical anthracites is given in the article coal.
Anthracite has a history of use in blast furnaces for iron smelting; however, it lacked the pore space of metallurgical coke, which eventually replaced anthracite.