#coal  fossil fuel consisting of carbonized vegetable matter deposited in the Carboniferous period
  supertype:  fossil_fuel  vegetable_matter
  substance:  carbon
  subtype:  anthracite_coal__anthracite__hard_coal  a hard natural coal that burns slowly and gives intense heat
  subtype:  bituminous_coal__soft_coal  rich in tarry hydrocarbons; burns readily with a smoky yellow flame
     subtype:  cannel_coal  a bituminous coal that burns with a luminous flame
     subtype:  sea_coal__seacoal  pulverized bituminous coal; used as a foundry facing
  subtype:  lignite__browncoal__wood_coal  intermediate between peat and bituminous coal
     subtype:  jet  a hard black form of lignite that takes a brilliant polish and is used in jewellery or ornamentation
  subtype:  steam_coal__steamcoal  coal suitable for use under steam boilers

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