COAL (LIGNITE, BITUMINOUS, ANTHRACITE)

ANTHRACITE, the highest rank; a harder, glossy, black coal used primarily for residential and commercial space heating. 

BITUMINOUS COAL, dense mineral, black but sometimes dark brown, often with well-defined bands of bright and dull material, used primarily as fuel in steam-electric power generation

SUB-BITUMINOUS COAL, whose properties range from those of lignite to those of bituminous coal are used primarily as fuel for steam-electric power generation

LIGNITE, also referred to as brown coal, is the lowest rank of coal and used almost exclusively as fuel for electric power generation.