A fissure is a crack in a gem, often open to the surface. Labs use the word for the cracks that fillers can enter.
In more detail
Almost all emeralds have fissures, and cutters plan around them. A surface-reaching fissure can weaken a stone. It also lets oil, resin or glass in, which makes it harder to see.
On a grading report
Filled fissures are reported with the filler and its degree: minor, moderate or significant.
Related terms
- Clarity enhancement: Clarity enhancement is filling surface-reaching fissures with a filler such as oil, resin, wax or glass, so they show less.
- Emerald oiling: Emerald oiling is filling an emerald's fissures with a colorless oil to make them less visible.
- Lead-glass filling: Lead-glass filling is a treatment that fills fissures and cavities in corundum, mostly ruby, with high-lead glass to hide them.
- Fingerprint: A fingerprint is a pattern of tiny fluid or glassy drops left where a crack inside the crystal healed. It often looks like a human fingerprint.
- Toughness: Toughness is a gem's resistance to chipping and breaking. It differs from hardness, which is resistance to scratching.