If a mineral breaks easily and cleanly in one or more directions, its cleavage is considered perfect. For example, calcite cleaves perfectly along three planes. As the quality of the break decreases, cleavage may be described as good, distinct, and poor or none. Some minerals cleave perfectly in one direction and poorly in others. For example, gypsum cleaves perfectly on one plane and poorly along two others.

Some common forms of cleavage:

Basal:

Cleavage exhibited on a horizontal plane of the mineral by way of its base. Minerals with basal cleavage can sometimes be "peeled".

Cubic:

Cleavage exhibited on minerals of the isometric crystal system crystallized as cubes. In this method of cleavage, small cubes evenly break off of an existing cube.

Octahedral:

Cleavage exhibited on minerals of the isometric crystal system crystallized as octahedrons. In this method of cleavage, flat, triangular "wedges" peel off of an existing octahedron.

Prismatic:

Cleavage exhibited on some prismatic minerals in which a crystal cleaves by breaking off thin, vertical, prismatic crystals off of the original prism.

Pinicoidal:

Cleavage exhibited on some prismatic and tabular minerals in which a crystal cleaves on the pinicoidal plane, which is the third dimension aside from the basal and prismatic sides.

Rhombohedral:

Cleavage exhibited on minerals crystallizing in the hexagonal crystal system as rhombohedrons, in which small rhombohedrons break off of the existing rhombohedron.