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The mineral property of cleavage is how a mineral breaks apart on a flat surface. Note that opposite sides of a mineral will always cleave the same. Cleavage can be described using:
How well it cleaves. There are five categories of this. The number used when listing is the same number when used to describe cleavage. For example. a mineral with cleavage one will have a perfect cleavage.
(1) Perfect: Minerals with perfect cleavage will have a completely smooth surface when they break apart.
(2) Good: Minerals with good cleavage will have a mostly smooth surface with some minor rough residual areas when they break apart.
(3) Poor: Minerals with poor cleavage will have mostly a rough surface when they break apart. The smooth side will not be as visible.
(4) Indiscernible: Minerals with indiscernible cleavage will exhibit small amounts of cleavage when they break apart, but nearly all the surface will be rough.
(5) None: Minerals with no cleavage will be completely rough and jagged when they break apart.
Cleavage can also be described by the number of directions (not sides) that cleave. The categories are:
○ One direction
○ Two directions
○ Three directions
○ All directions.
Cleavage is measured when you add the quality of the cleavage with the number of sides it cleaves on. For example, a mineral with a cleavage of 1,3 will cleave perfectly in 3 directions. Also, a mineral with a cleavage of 1,1 ; 2,2 will cleave perfectly on 2 sides (1 direction) and have a good cleavage on the other 4 sides (2 directions.
Cleavage can also be described using cleavage habit. These are the forms of cleavage and include:
○ Basal cleavage: This is cleavage by the shape of the base. Minerals with this kind of cleavage may be able to be "peeled."
○ Cubic cleavage: This is cleavage in the shape of a cube. In this cleavage, small cubes break off a bigger cube.
○ Octahedral Cleavage: In this cleavage. flat triangular "wedges" peel off of an octahedron. (a 3-dimensional object with 8 sides consisting of entirely triangles)
○ Prismatic Cleavage: In this cleavage, prismatic crystals break off a bigger prism.
○Rhombohedral Cleavage: In this cleavage, small rhombohedrons break off a bigger rhombohedron. A rhombohedron is a six-sided figure in which side is a rhombus. (basically a tilted cube)