What Is Gemstone Cleavage
Wood is easier to split with grain than against it, gemstone cleavage can be found in the gemstone. It is the tendency of certain crystal to break along definite plane surfaces. If you find planes in crystal structure with weak atomic bond, the crystal is more likely to break along those planes.
The atomic arrangement within a crystal is symmetrical in shape, the planes of specific bonds could be found in symmetrically disposed within the crystal. Internal cleavage is also present inside, are, therefore, as symmetrical as external crystal faces.
What is actually mean by cleavage?
The term cleavage in gemology means to crystalline materials. As for example, since glass is a super cooled liquid in which the atoms are not arranged in long-range periodic manner. It can have no cleavage because there are no uniform bond layers.
Various Cleavage Grades
Gemstone cleavage varies and is usually described with reference to crystallographic axes and directions and is also graded as per its ‘perfection’, or ease with which the gem can be split along the cleavage.
There are five grades or degrees on which the cleavage differs:
Poor or weak
Fair or moderate
Good or imperfect
Gems which have perfect cleavage are easy to spit, while those with no cleavage are hardest but within the same crystal. Sometimes, we can find various degrees of cleavage perfection but found in different directions.
Can Gemstone Cleavage Affect Jewelry Setting?
Gems with perfect cleavage should be set and worn carefully because sharp blow to the stone along a cleavage direction could split the gem. The gem Spodumene is popular for having difficulty in cutting. Even there is a problem in cutting topaz and offers occasional problems to the cutter who is not well-aware of its cleavage pattern and direction. It is virtually impossible to polish a gemstone surface that is parallel to a cleavage plane.
This term refers to the fibrous and splintery fracture and is often used interchangeably to denote a fracture which creates sharp and elongated points in a mineral.
This fracture produces sharp, jagged points.
This fracture produces a rough, uneven surface and uneven fractures don’t have sharp points like splintery.
This term refers to breakage of minerals along directions of structural weakness as twinning.
But unlike cleavage, parting isn’t found in all species of gemstone. Parting is a result of the individual growth of a particular gemstone and not the atomic or crystal structure of the gem.