Diamond Symmetry is the term that describes how precisely the facets of a diamond align and intersect. Problems can include extra facets or misshapen facets, off center culets or tables, and wavy girdles. The more symmetry problems in a diamond, the more problematic the light traveling through the diamond becomes. Misdirected light can adversely affect the diamond's brilliance. symmetry may misdirect light that travels into the diamond, sending it off at slightly wrong angles, and thereby reducing the diamond's brilliance. There are often trade-offs here when a diamond cutter may purposely create a minor asymmetry in order to prevent a defect present in the rough stone from being retained as part of the finished diamond.
The diamond symmetry
grade as determined by the GIA uses the following scale:1. Excellent: No symmetry defects visible at 10x magnification 2. Very Good: Any defects are very difficult to see at 10x magnification 3. Good: Defects are difficult to see at 10x magnification 4. Fair: Defects are visible at 10x magnification and may be visible without magnification 5. Poor: Defects are visible without magnificationFor diamonds with a symmetry grade of Excellent to Good, symmetry should not be used as a primary factor in choosing a diamond, since each of these grades is possible in diamonds of exceptional appearance. Symmetry is more important in diamonds of VVS2 Clarity and higher, since the very subtle defects produced by Fair or Poor symmetry (which can resemble pinpoint inclusions) would compromise the diamond's otherwise flawless appearance.Despite its modest impact on appearance, diamond symmetry has a significant impact on price; a diamond with Excellent Symmetry and Polish may be priced 10%-15% higher than a diamond with Good Symmetry and Polish. This premium has more to do with consumer's perceived value of "excellent" grades, than the actual effect on a diamond's appearance.Because Poor diamond symmetry have defects visible to the naked eye, these diamonds should be avoided in all cases.A diamond should not be chosen or rejected based solely on symmetry. Because the overall Diamond Cut
grade already incorporates symmetry, it should be used as the primary determinant when choosing a diamond. When comparing two diamonds of equal Cut grade, diamond symmetry (and polish) can then be used as a further refinement or tie breaker.