#fossil_fuel  fuel consisting of the remains of organisms preserved in rocks in the earth's crust with high carbon and hydrogen content
  supertype:  #fuel__combustible__combustiblematerial  a substance that can be burned to provide heat or power; "more fuel is needed during the winter months"; "they developed alternative fuels for aircraft"
  subtype:  #coal  fossil fuel consisting of carbonized vegetable matter deposited in the Carboniferous period
     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
  subtype:  #natural_gas__gas  a fossil fuel in the gaseous state; used for cooking and heating homes
  subtype:  #petroleum__crude_oil__crudeoil__crude__coal_oil__rock_oil__fossil_oil  a dark oil consisting mainly of hydrocarbons

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