Like polish, symmetry is graded from 'Excellent' down to 'Poor'. If a diamond has poor symmetry, the facet edges and points sit at slight angles – causing light to 'leak' out through the bottom or sides instead of being reflected up to the eye. The result is a weaker, uneven brilliance and a 'dead' center in the stone.

GIA grades symmetry in five levels:

• Excellent: Facet placement is perfectly aligned – no asymmetry detectable under 10x magnification. Light flows evenly and symmetrically.

• Very Good: Very minor deviation, barely noticeable even for experts. Virtually as good as Excellent.

• Good: Minor asymmetry under 10x magnification but no visible impact to the naked eye.

• Fair: Clear asymmetries under 10x magnification that can affect light distribution.

• Poor: Obvious asymmetry leading to uneven light distribution and noticeably weaker brilliance.

Certain round brilliants with Excellent symmetry and polish form a characteristic optical pattern: eight perfect hearts visible from below and eight arrows visible from above in a special H&A viewer. These 'Super Ideal' cut diamonds represent the absolute peak of cutting precision. They are rare, premium-priced, and highly sought after by diamond enthusiasts and collectors worldwide.