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Cleavage

Cleavage can be described as the manner that a mineral tends to break and is closely related to fracture but is not the same, a mineral can have a weak zones that a crack follows, these zones are parallel to a crystal face and reflects the crystal symmetry, thus the direction of the break is controlled by the symmetry of the crystal, cleavage is reproducible, you can break a mineral over and over again along the same plane, its like the mineral were formed by invisible layers of the same material bond with a weaky invisible glue and when the piece is broken, the crack always will follow the glued bonds, minerals that have no cleavage only can show fractures when are broken. Cleavage along hardness is an important tool used to the identification of minerals.

 
Fluorite
Luis Lyons photo
Quartz
Luis Lyons photo
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