In embryology, cleavage is the division of cells in the early embryo. The zygotes of many species undergo rapid cell cycles with no significant growth, producing a cluster of cells the same size as the original zygote.
In mineralogy, the tendency of crystalline materials to split along definite planes, creating smooth surfaces, of which there are several named types:
Basal cleavage: cleavage parallel to the base of a crystal, or to the plane of the lateral axes.
Cubic cleavage: cleavage parallel to the faces of a cube.
Diagonal cleavage: cleavage parallel to a diagonal plane.
Lateral cleavage: cleavage parallel to the lateral planes.
Cleavage is the property of a mineral that allows it to break smoothly along specific internal planes (called cleavageplanes) when the mineral is struck sharply with a hammer.
Thus a mineral's cleavage may be described as perfect three planecleavage, in which case the mineral breaks with almost mirror-like surfaces along the three dimensional axes; the mineral calcite exhibits such cleavage.
Cleavage tendencies and patterns are also useful in the cutting of gem stones, the growth and utilization of silicon chips, and the production of synthetic crystals for use in lasers.
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