<P> Precious stones are generally cleaved by impact, as in diamond cutting . </P> <P> Synthetic single crystals of semiconductor materials are generally sold as thin wafers which are much easier to cleave . Simply pressing a silicon wafer against a soft surface and scratching its edge with a diamond scribe is usually enough to cause cleavage; however, when dicing a wafer to form chips, a procedure of scoring and breaking is often followed for greater control . Elemental semiconductors (Si, Ge, and diamond) are diamond cubic, a space group for which octahedral cleavage is observed . This means that some orientations of wafer allow near - perfect rectangles to be cleaved . Most other commercial semiconductors (GaAs, InSb, etc .) can be made in the related zinc blende structure, with similar cleavage planes . </P>

Why do we use two terms to describe cleavage