#biotite  dark brown to black mica found in igneous and metamorphic rock
  supertype:  #mica__isinglass__isinglas  any of various minerals consisting of hydrous silicates of aluminum or potassium etc. that crystallize in forms that allow perfect cleavage into very thin leaves; used as dielectrics because of their resistance to electricity
  subtype:  #lepidomelane  a mica that is a biotite containing iron

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