Chip (6.21)
Since diamond is such an incredibly hard substance, it is susceptible to chipping. A very hard substance is not necessarily a very tough substance. When it breaks, it breaks suddenly, leaving jagged, uneven edges. A diamond’s fracture is classified as uneven since after the damage occurs, it leaves an unsymmetrical, step-like surface. However, chips that occur along the cleavage plane (parallel to the triangular octahedral faces) leave a smooth, almost facet-like surface. Naturals (discussed later) are often mistaken for chips and vice versa.
A chip is an excellent way to authenticate diamond. No other imitations leave a chip like diamond’s. Conchoidal (pronounced kahn-koy’-dal) is a smoother, rounded or shell-like fracture that occurs in other stones and once identified you can feel confident that the stone in question is not diamond.
A chip is considered much more serious than a nick, which is smaller and less noticeable. Generally a chip requires considerable weight loss in re-cutting to bring the stone back to salable condition. A chip can occur anywhere on a diamond, but it is most common on or around the girdle. The girdle is most apt to chip since it is exposed in most settings, and it is the apex of the acute angle formed between the pavilion (bottom) and crown (top). With acute angles there is more danger of damage than with obtuse angles, as between the table and the stars or crown main facets. This is why it is important for the cutter to leave at least a thin girdle, avoiding extremely thin, to protect the stone from the hazards of everyday wear or even from mishandling with tweezers. The ultimate accident waiting to happen, is a combination of flat crown angles, flat pavilion angles, and an extremely thin girdle containing a feather on or close to its surface. This scenario inevitably results in disaster. Why would a cutter leave such a situation on a diamond? Simply put -- weight retention and perhaps carelessness.