A round brilliant is a round diamond with the brilliant facet plan. It has 33 crown and 24 pavilion facets: 57 in all, or 58 with a culet.
In more detail
It is the most common shape. GIA gives a cut grade only to standard round brilliants in the D-to-Z range. Most are now finished with a faceted girdle, which is counted separately. Its proportions go back to Tolkowsky's 1919 calculation.
On a grading report
Written "Round Brilliant" in the shape and cutting style line.
Related terms
- Brilliant cut: A brilliant cut is a cutting style with a crown of facets above a pavilion. Its facet angles return light and spread it into fire.
- Tolkowsky ideal cut: The Tolkowsky ideal cut is the round brilliant that Marcel Tolkowsky calculated in his 1919 book Diamond Design. It has a 40.75° (40° 45′) pavilion, a 34.5° (34° 30′) crown and a 53% table.
- 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.
- Facet: A facet is one flat, polished face of a cut gemstone. Its angle and its direction around the stone decide where it sends light.
- Fancy shape: A fancy shape is any diamond outline other than round, such as oval, pear, marquise, cushion, princess or emerald.