CLEAVAGE

The internal arrangement of atoms within a crystalline material (the crystal structure) has a regular three-dimensional pattern. The atoms may be bonded in a number of differ­ent ways, with bonds of different strengths. As a result, the crystal may have one or more planes or directions of relative weakness along which it will break more easily. These are called 'directions of cleavage'. When a crystalline material breaks along a cleavage plane, it will leave a flat, or nearly flat, cleavage surface. Cleavage can only occur in crystalline materials and may be defined as perfect, good, fair, or poor.

diamond is the hardest gemstone, but with a well-aimed hit, it is possible to break a diamond in two with a clean break. The clean break occurs along one of its three perfect cleavage planes.

This ability to cleave is taken into account during the fashioning of a diamond, and may be the first step in the process of cutting. The ease with which a gemstone cleaves and the number of cleavage directions it possesses is also important with regard to its durability and its identification.