Cleavage (crystal)

  Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite planes, creating smooth surfaces, of which there are several named types:

• Basal cleavage: cleavage parallel to the base of a crystal, or to the plane of the lateral axes. This occurs quite easily in graphite, making the material feel slippery.

• Cubic cleavage: cleavage parallel to the faces of a cube. This is the source of the cubic shape seen in crystals of ground table salt (sodium chloride).

• Diagonal cleavage: cleavage parallel to a diagonal plane.

• Lateral cleavage: cleavage parallel to the lateral planes.

• Octahedral, Dodecahedral, or Rhombohedral cleavage: cleavage parallel to the faces of an octahedron, dodecahedron, or rhombohedron (respectively). Octahedral cleavage is seen in common semiconductors (see below).

• Prismatic cleavage, cleavage parallel to a vertical Prism.