rhombohedral cleavage

Cleavage \Cleav"age\, n.
   1. The act of cleaving or splitting.
      [1913 Webster]

   2. (Crystallog.) The quality possessed by many crystallized
      substances of splitting readily in one or more definite
      directions, in which the cohesive attraction is a minimum,
      affording more or less smooth surfaces; the direction of
      the dividing plane; a fragment obtained by cleaving, as of
      a diamond. See {Parting}.
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   3. (Geol.) Division into lamin[ae], like slate, with the
      lamination not necessarily parallel to the plane of
      deposition; -- usually produced by pressure.
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   {Basal cleavage}, cleavage parallel to the base of a crystal,
      or to the plane of the lateral axes.

   {Cell cleavage} (Biol.), multiplication of cells by fission.
      See {Segmentation}.

   {Cubic cleavage}, cleavage parallel to the faces of a cube.
      

   {Diagonal cleavage}, cleavage parallel to ta diagonal plane.
      

   {Egg clavage}. (Biol.) See {Segmentation}.

   {Lateral cleavage}, cleavage parallel to the lateral planes.
      

   {Octahedral cleavage}, {Dodecahedral cleavage}, or
   {Rhombohedral cleavage}, cleavage parallel to the faces of an
      octahedron, dodecahedron, or rhombohedron.

   {Prismatic cleavage}, cleavage parallel to a vertical prism.
      [1913 Webster]