#metamorphic_rock__metamorphicrock  rock altered by pressure and heat
  supertype:  rock__stone  material consisting of the aggregate of minerals like those making up the Earth's crust
  subtype:  amphibolite  a metamorphic rock composed chiefly of amphibole and plagioclase
  subtype:  marlite__marlstone  metamorphic rock with approximately the same composition as marl
  subtype:  hornfels__hornstone  a fine-grained metamorphic rock formed by the action of heat on clay rocks
  subtype:  gneiss  a laminated metamorphic rock similar to granite
  subtype:  schist  any metamorphic rock that can be split into thin layers

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