Difference between revisions of "Cleavage"
From The Gemology Project
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+ | ==Cleavage== | ||
+ | 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.<br /> | ||
+ | |||
+ | 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 | ||
[[image:cleavage_prismatic.jpg|left|thumb|200px|Prismatic cleavage]] | [[image:cleavage_prismatic.jpg|left|thumb|200px|Prismatic cleavage]] | ||
[[image:cleavage_basal.jpg|left|thumb|200px|Basal cleavage]] | [[image:cleavage_basal.jpg|left|thumb|200px|Basal cleavage]] | ||
+ | <br clear="all" /> | ||
+ | |||
+ | ==Parting== | ||
+ | |||
+ | Parting is the splitting of a gemstone along twinning planes. | ||
+ | |||
+ | ==Fracture== | ||
+ | |||
+ | 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).<br /> | ||
+ | |||
+ | The types of fracture are: | ||
+ | * conchoidal | ||
+ | * uneven | ||
+ | * even |
Revision as of 14:49, 9 December 2006
Contents
Cleavage
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
Parting
Parting is the splitting of a gemstone along twinning planes.
Fracture
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