Types and classification of coal

As geological processes apply pressure to dead plant material, over time it is transformed into the following:

• Peat – this is not yet coal

  

• Lignite, or brown coal, the lowest rank of coal, used almost exclusively as fuel for electric power generation. Jet is a compact form of lignite that is sometimes polished and has long been used as an ornamental stone

  

• Sub-bituminous coal is used as fuel for steam-electric power generation

  

• Bituminous coal is a dense sedimentary rock, usually black, but sometimes dark brown. It is used primarily as fuel in steam-electric power generation, or heat and power applications in manufacturing and to make coke

  

• Steam coal was once widely used as a fuel for steam locomotives, where it is sometimes known as ‘sea coal’

  

• Anthracite is the highest rank of coal. It is a harder, glossy black coal used primarily for residential and commercial space heating

  

• Graphite is no longer coal. It is difficult to ignite and not commonly used as fuel; it is most used in pencils, or powdered for lubrication