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Cleavage and Fracture

Minerals aren't always found as perfect crystals -- they are often partially or completely broken into smaller parts. Just how they break apart is an important identifying characteristic. If when they break they form flat surfaces, they are said to have cleavage. If they form non-flat surfaces, they have fracture.

Common Cleavage Patterns
Octahedral (4 cleavage planes)
Cubic (3 cleavage planes @ 90 degrees)
Rhombahedral (3 cleavage planes NOT @ 90 degrees)
Prismatic (2 cleavage planes / 3rd direction shows fracture)
Pinacoidal (1 cleavage plane / other two directions show fracture - produces flat sheets)
Common Fracture Patterns
Conchoidal (shell-like)
Fibreous (narrow splinters)
Hackly (jagged edges)
Uneven (rough)

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