Coal in a Nutshell
WEBJan 23, 2020 · With more heat and pressure lignite releases more hydrocarbons and becomes the highergrade bituminous coal. Bituminous coal is black, hard and usually dull to glossy in appearance. Still greater heat and pressure yields anthracite, the highest grade of coal. In the process, the coal releases methane or natural gas. Anthracite, a .