6.1: Cleavage
- Page ID
- 3200
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Cleavage is the splitting of a gemstone along the direction of its crystal faces where atoms have weaker bonding. This can occur only in crystalline minerals when a precise blow is given in a particular direction. The result of cleavage is a more or less flat plane with often a silky luster.
Cleavage is a reproducible property of a gemstone and can be done at any point of the cleavage direction.
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 (or imperfect)
- Fair (or moderate)
- Poor (or weak)
- None
Figure \(\PageIndex{1}\): Prismatic cleavage
Figure \(\PageIndex{2}\): Basal cleavage
Stones and their cleavage directions:
Table \(\PageIndex{1}\)
Cleavage | Directions | Stones | Quality |
---|---|---|---|
Basal | 1 | Topaz | Perfect |
Beryl | Imperfect | ||
Prismatic | 2 | Peridot | Perfect |
Spodumene | Perfect | ||
Chrysoberyl | Weak to Moderate | ||
Diopside | Perfect | ||
Cubic | 3 | Halite | Perfect |
Rhombohedral | 3 | Calcite | Perfect |
Rhodochrosite | Perfect | ||
Octhahedral | 4 | Fluorite | Perfect |
Diamond | Perfect | ||
Dodecahedral | 6 | Sphalerite | Perfect |
Sources
- Gemmology 3rd edition (2005) - Peter Read