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.
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: