Anthracite

Anthracite, often referred to as hard coal, 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 and is the highest ranking of coals.Anthracite derives from the Greek anthrakítēs (ἀνθρακίτης), literally 'coal-like'. Other terms which refer to anthracite are black coal, hard coal, stone coal, dark coal, coffee coal, blind coal (in Scotland), Kilkenny coal (in Ireland), crow coal or craw coal, and black diamond. 'Blue Coal' is the term for a once-popular and trademarked brand of anthracite, mined by the Glen Alden Coal Company in Pennsylvania, and sprayed with a blue dye at the mine before shipping to its northeastern U.S. markets to distinguish it from its competitors.Anthracite is similar in appearance to the mineraloid jet and is sometimes used as a jet imitation.In southwest Wales, anthracite has been burned as a domestic fuel since at least medieval times, when it was mined near Saundersfoot. More recently, large-scale mining of anthracite took place right across the western part of the South Wales Coalfield until the late 20th century. Mining continues but now on a smaller scale.Anthracite generally costs two to three times as much as regular coal. In June 2008, the wholesale cost of anthracite was US$150/short ton.Anthracite is processed into different sizes by what is commonly referred to as a breaker. The large coal is raised from the mine and passed through breakers with toothed rolls to reduce the lumps to smaller pieces. The smaller pieces are separated into different sizes by a system of graduated sieves, placed in descending order. Sizing is necessary for different types of stoves and furnaces.Historically from time to time, underground seams of coal have caught fire, often from careless or unfortunate mining activities. The pocket of ignited coal is fed oxygen by vent paths that have not yet been discovered. These can smolder for years. Commonly, exhaust vents in populated areas are soon sensed and are sealed while vents in uninhabited areas remain undiscovered. Occasionally, vents are discovered via fumes sensed by passers-by, often in forested areas. Attempts to extinguish those remaining have at times been futile, and several such combustion areas exist today. The existence of an underground combustion site can sometimes be identified in the winter where fallen snow is seen to be melted by the warmth conducted from below. Proposals for harnessing this heat as geothermal energy have not been successful.Among current producers, Russia, China and Ukraine have the largest estimated recoverable reserves of anthracite. Other countries with substantial reserves include Vietnam and North Korea.Attribution: