Anthracite

Anthracite is the most metamorphosed type of coal (but still represents low-grade metamorphism), in which the carbon content is between 92.1% and 98%.[|[][|2][|]][|[][|3][|]] 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 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].
 * Anthracite** ([|Greek] //aνθρακίτης (anthrakítes),// "coal-like," from //άνθραξ (ánthrax),// coal)[|[][|1][|]] is a hard, compact variety of mineral [|coal] that has a high [|luster]. It has the highest [|carbon] count, the fewest impurities, and the highest calorific content of all types of coals, which also include [|bituminous coal] and [|lignite].

History:

Birth of anthracite. Material was deposited that eventually transforms to anthracite coal. This occurred during the Carboniferous Geologic Period. At that time, most of Pennsylvania was a flat, hot, moist plain covered with steaming swamps thick with tall trees and wide spreading ferns.