Symmetry is the report grade, from Excellent to Poor, for the exactness of a stone's outline. It also covers the shape, placement and alignment of the facets.
In more detail
GIA sorts the faults into two kinds. Proportion faults include an off-center table or culet; facet faults include extra or misshapen facets. On a GIA round, Good symmetry limits the cut grade to Very Good, Fair to Good and Poor to Poor. Our Hearts & Arrows Scope and Cut Performance Wheel have their own symmetry measure, not the report grade.
On a grading report
In the additional grading section of GIA and IGI reports. IGI gives a symmetry grade for every shape and color.
Related terms
- Polish: Polish is the grade for the smoothness of the facet surfaces, from Excellent to Poor. The grader looks at 10x for pits, nicks, polish lines, scratches, burn marks and rough patches.
- Cut grade: The cut grade rates how well a diamond's proportions and finish work, from Excellent to Poor. GIA gives it only to standard round brilliants in the D-to-Z color range.
- Hearts and arrows: Hearts and arrows is a pattern that a precisely cut round brilliant shows in a reflector viewer. Face-up it shows eight arrows, and face-down eight hearts.
- Triple Excellent: Triple Excellent is trade shorthand for a GIA round brilliant with Excellent cut, Excellent polish and Excellent symmetry.
- Extra facet: An extra facet is a facet that the cutting style doesn't need, placed without regard for the stone's symmetry. It is most often near the girdle.