What is Cleave

A cleave occurs when a gemstone breaks along a plane dictated by its crystalline atomic structure.


When gemstones cleave, they do so along planed surfaces. The crystalline formation of gemstones creates a symmetrical atomic arrangement along which the stones have enough structural weakness to split. The arrangement of atoms dictates the direction and axis of cleavage possible within a rough stone and also creates a potential hazard for unwanted cleavage during additional shaping or polishing.

Cleaving rough diamonds

The molecular makeup of a rough diamond gives each face a triangular octahedral structure. The symmetry of the crystalline structure means internal cleavage planes along which a cleaver could split the stone occur parallel to the outside faces. This makes it possible to cleave each face of a diamond in four potential directions. In the case of large gemstones, cleavers may face difficulty in deciding where to split the stone to retain maximum value. In some cases, stones can provide more value when split into multiple smaller gems. In other cases, a cleaver may wish to maximize the overall size of the stone.

Cleavage as investment risk

Properly done, cleavage gives a basic form to a rough gemstone. Further steps to create a finished stone may involve additional cutting, polishing and faceting. After successful cutting and polishing, the value of a gemstone typically increases. Since larger gemstones tend to be rare, their value can increase substantially after cutting and polishing. This potential profit attracts gemstone investors, who see an opportunity to buy a relatively inexpensive rough stone and sell it at a large profit after contracting to have it cut and polished. However, gemstone investments include the risk that a stone will cleave or even shatter during the cutting or polishing process, causing a substantial decrease in its value.

Different gems exhibit different characteristics which make them more or less prone to cleavage. Jewelers recognize a range of grades that correspond to the ease with which a gemstone will split along a cleavage line. A “perfect” cleavage grade indicates a gem will split easily, while a grade of “none” means a gem will not cleave under any circumstances. For example, opal, onyx and ruby stones do not cleave. Stones with perfect cleavage planes include diamonds, moonstone and topaz. In between lie stones such as tourmaline, emerald and lapis lazuli.

Investors who wish to profit from cutting and polishing rough stones should understand the risk of cleavage, research the type of gems available for purchase in rough form and choose skilled jewelers to cut, polish and facet the stones.