Adventist Youth Honors Answer Book/Nature/Rocks & Minerals/Cleavage
Cleavage 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.
- 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 used in electronics.
- Prismatic cleavage, cleavage parallel to a vertical prism.
Cleavage is of technical importance in the electronics industry and in the cutting of gemstones. While precious stones are generally cleaved by impact, man-made single crystals of semiconductor materials are generally sold as thin wafers which are much easier to cleave. Simply pressing a silicon wafer against a soft surface and scratching its edge with a diamond scribe is usually enough to cause cleavage.