brown coal

…When coal in the broad sense is divided into two categories according to its degree of coalification, brown coal is the one with a low degree of coalification, and coal in the narrow sense is the one with a high degree of coalification. In this case, brown coal includes subbituminous coal (the one with the higher degree of coalification) and lignite (the one with the lower degree of coalification) when coal in the broad sense is divided into four stages according to its degree of coalification (anthracite, bituminous coal, subbituminous coal, brown coal). In Japan, these four categories are also used, but the term brown coal is not usually used. Brown coal with a particularly low degree of coalification is called lignite, and the rest are collectively called coal. …

*Some of the terminology that refers to "brown coal" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…広義の石炭を石炭化度によって二大別するとき，石炭化度の低い範囲のものを褐炭，高い範囲のものを狭義の石炭という。この場合の褐炭brown coalは，広義の石炭を石炭化度によって4段階(無煙炭，歴青炭，亜歴青炭，褐炭)に区分をしたときの亜歴青炭(石炭化度の高いほう)と狭義の褐炭lignite(低いほう)を包含する。日本でもこの4区分はあるが，普通は褐炭という呼び方はされず，褐炭のうち，とくに石炭化度の低いものを亜炭とし，それ以外は石炭と総称している。…

※「brown coal」について言及している用語解説の一部を掲載しています。

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