Cleave

What Does Cleave Mean?
The occurrence of a gemstone breaking into two or more pieces during the cutting or polishing process. Naturally occurring impurities in the stones increase the likelihood that a stone will break apart.

Investopedia explains Cleave
Gemstones - especially large ones - are very rare. When large gemstones are found, they are usually sold to investors who pay to have the stones cut and polished. A large gemstone that is successfully cut and polished is many times more valuable than an unpolished stone of similar size. However, gemstone investments include the substantial risk that a stone will cleave during the cutting or polishing process, causing a substantial decrease in its value.