From The Gemology Project
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Cleavage is the splitting of a gemstone along the direction of its crystal faces where molucules have weak bonding. This can occur only in crystalline minerals when a precise blow is given in a particular direction, even if the habit does not show the crystal faces. The result of cleavage is a more or less flat plane with often a silky luster.

There are several directions of cleavage.

  • Prismatic cleavage
  • Basal cleavage
  • Pinacoidal cleavage
  • Octahedral cleavage
  • Rhombohedral cleavage

The quality of cleavage is expressed with a few simple phrases.

  • Perfect
  • Good
  • Fair
  • Poor
Prismatic cleavage
Basal cleavage


Parting is the splitting of a gemstone along twinning planes.


Fracture is the random breakage of a gemstone when behing hit with a sharp or hard object. The most common type of fracture is termed "conchoidal" (shell-like).

The types of fracture are:

  • conchoidal
  • uneven
  • even