# 6.1: Cleavage

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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

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