cleavage, tendency of many minerals to split along definite smooth planar surfaces determined by their crystal structure. The directions of these surfaces are related to weaknesses in the atomic structure of the mineral and are always parallel to a possible crystal face. The property of cleavage is useful in identifying a mineral species. The tendency for certain varieties of metamorphic and sedimentary rock to split along more or less smooth surfaces is sometimes referred to as rock cleavage. Flagstone, slate, and schist are noted for this property, which arises from the parallel alignment of fine, platy mineral grains, themselves displaying cleavage.

Tendency of a crystalline substance to split into fragments bounded by plane surfaces. Cleavage surfaces are seldom as flat as crystal faces, but the angles between them are highly characteristic and valuable in identifying a crystalline material. Cleavage occurs on planes where the atomic bonding forces are weakest; for example, galena cleaves parallel to all faces of a cube. Cleavage is described by its direction (as cubic, prismatic, basal) and by the ease with which it is produced. A perfect cleavage produces smooth, lustrous surfaces. Other degrees include distinct, imperfect, and difficult. Seealso fracture.

Learn more about cleavage with a free trial on Britannica.com.

Cleavage in general refers to a division or separation of form. Its usage is heavily dependent on cultural context, where it may refer to:

• Partial exposure of part of the body:
• Cleavage (breasts), partial exposure of the separation between a woman's breasts.
• Cleavage enhancement, methods of making a person's breast cleavage look better than it really is.
• Buttock cleavage
• Toe cleavage
• Cleavage (crystal), in mineralogy and materials science, is a process of splitting a single crystal.
• Cleavage (geology), Foliation perpendicular to stress as a result of ductile deformation. e.g. shales (shists)
• Cleavage (embryo), in embryology, is the division of cells in the early embryo.
• Cleavage (fiber), in optical fibers.
• Teeth cleavage or tooth cleavage, slang for Diastema (dentistry), the gap between a person's two front teeth.
• In cell biology, the Cleavage furrow is the indentation that begins the process of cleavage, by which animal cells undergo cytokinesis.
• Bond cleavage in chemistry and biochemistry
• Cleavage (politics) The divisions of society that cause people to vote differently