Cleavage

The act of cleaving or splitting.

The quality possessed by many crystallized substances of splitting readily in one or more definite directions, in which the cohesive attraction is a minimum, affording more or less smooth surfaces; the direction of the dividing plane; a fragment obtained by cleaving, as of a diamond. See Parting.

Division into laminae, like slate, with the lamination not necessarily parallel to the plane of deposition; -- usually produced by pressure.

the breaking of a chemical bond in a molecule resulting in smaller molecules