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
    Peat [photo]
  • 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

    Lignite [photo]
  • Sub-bituminous coal is used as fuel for steam-electric power generation

    Sub-bituminous coal [photo]
  • 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

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

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

    Anthracite [photo]
  • 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

    Graphite [photo]


Thermal v metallurgical coal: the most important coal classification

Coal classificationUse of coal

Thermal coal
Other name: steam coal

Burnt to generate electricity via steam

Metallurgical coal
Other name: coking coal

Burnt at a high temperature to make steel