Anthracite - Properties

Properties

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, its higher relative density of 1.3–1.4, and lustre, 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 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 steam electric power generation.

Anthracite may be considered to be a transition stage between ordinary bituminous 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 earth-movements, such as the flanks of great mountain ranges. Anthracite is a product of metamorphism and is associated with metamorphic rocks, just as bituminous is associated with sedimentary rocks. For example, the compressed layers of anthracite that are deep mined in the folded (metamorphic) Appalachian Mountains of the Coal Region of northeastern Pennsylvania are extensions of the layers of bituminous coal that are strip mined on the (sedimentary) Allegheny Plateau of Kentucky and West Virginia, 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, it 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 feeling perceptibly colder when held in the warm hand than a similar lump of bituminous at the same temperature. The chemical composition of some typical anthracites is given in the article coal.