Anthracite

Anthracite, also known as hard coal and black coal, is a hard, compact variety of coal that has a submetallic lustre. 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.

The Coal Region of Northeastern Pennsylvania in the United States has the largest known deposits of anthracite coal in the world with an estimated reserve of seven billion short tons (6.35 billion metric tons). China accounts for the majority of global production; other producers include Russia, Ukraine, North Korea, South Africa, Vietnam, Australia, Canada, and the United States. The total production of anthracite worldwide in 2023 was 632 million short tons (573 million metric tons).

Anthracite is the most metamorphosed type of coal, but still represents low-grade metamorphism, in which the carbon content is between 86% and 97%. 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 is difficult to ignite, and burns with a short, blue, and smokeless flame.

Anthracite is categorized into several grades. Standard grade anthracite is used predominantly in power generation, and high grade (HG) and ultra high grade (UHG) are used predominantly in the metallurgy sector. Anthracite accounts for about 1% of global coal reserves, and is mined in only a few countries around the world.

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.

Culm has different meanings in British and American English. In British English, culm is the imperfect anthracite, located predominantly north Devon and Cornwall, which was used as a pigment. The term is also used to refer to some carboniferous rock strata found in both Britain and in the Rhenish hill countries, also known as the Culm Measures. In Britain, it may also refer to coal exported from Britain during the 19th century. In American English, "culm" refers to the waste or slack from anthracite mining, mostly dust and small pieces not suitable for use in home furnaces.

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 green 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.