T105 Round Brilliant Peridot: more facets, more sparkle
Brilliance 84 · Fire 53 · Scintillation 90 · in our census, where the T73 scores 90 · 53 · 80 in peridot
How the T105 Round Brilliant handles light in peridot, measured: brilliance 84, fire 53 and 16% leakage, set against the T73 in the same stone and against the same cut in diamond.
Light Return map of the T105 Round Brilliant in peridot, face-up, from our own tracer at refractive index 1.65. Red, green and blue return light to the eye; gray leaks.
T105 Round Brilliant Peridot
Peridot has a refractive index of 1.650 to 1.690 and a dispersion of 0.020. Its critical angle, from the low end of that range, is 37.3°, so a round design needs a pavilion of at least 37.3° for head-on light to reflect off both sides of the pavilion and leave through the table. We trace it with one index, 1.670, the midpoint of the published range, and a fire spread of 0.017, 0.86 of the published dispersion. Every picture here is our Light Return tracer at 1.650, and every figure is from the same light census that scores the other gemstones; the 3D Gemstone Simulator shows the T105 Round Brilliant in peridot live. Peridot is strongly doubly refractive (birefringence up to 0.038), so its back facets can look doubled. Our census traces one index (1.670), so the doubling is not in these figures.
The T105 Round Brilliant has 105 facets and a total depth of 59.3% of its width; its pavilion mains sit at 40.8°. In peridot, the census returns 84 of 100 for brilliance and 53 for fire, against 90 and 53 for the T73, our benchmark, in the same stone; the same T105 Round Brilliant in diamond reads 95 and 77.
Is peridot good in a T105? Pros and cons, measured
Compared with the T73 Round Brilliant in peridot and with the T105 Round Brilliant in diamond.
A difference counts from 3 points (Brilliance, Fire, Tilt, Leakage), 5 (Scintillation,
Symmetry), 4% (face-up size per carat) or 5% (weight); Tilt counts as a pro only for a stone within
5 points of the brilliance it is compared with. How we measure.
All eight scores against the T73
At a glance: the T105 Round Brilliant in peridot (white) against the T73 Round Brilliant in peridot (dashed): solid white where
it reaches further, hatched where it falls short. Each pro and con is explained, with pictures, below.
Against the T73 Round Brilliant in peridot: ahead on 3, level on 2, behind on 3.
Global79, the comparison 80, difference −1
Brilliance84, the comparison 90, difference −6
Fire53, the comparison 53, difference 0
Scintillation90, the comparison 80, difference +10
Spread101, the comparison 100, difference +1
Symmetry100, the comparison 100, difference 0
Shape-norm91, the comparison 97, difference −6
Tilt77, the comparison 74, difference +3
Face-up light census, a different measure from the Cut Grading Tool; Spread and Shape-norm above 100 sit on the ring. Spread is the census's estimate from depth alone; the face-up size in the pros and cons is measured from each model's outline. Open it in the Cut Performance Wheel; these are the same census figures as our Cut Performance Index.
What the T105 Round Brilliant gains in peridot
More facets, more sparkle
Scintillation 90 against 80 for the T73 Round Brilliant in peridot: 10 points higher
Scintillation follows the number of facets the stone shows: 100 × (1 − e^(−facets / 45)). The T105 Round Brilliant has 105 facets and the T73 73, so 90 against 80. It depends on the geometry alone, so it is the same in every stone.
Scintillation follows the number of facets: more facets, more and smaller flashes as the stone moves. Compare the facet counts under the drawings; each drawing shows only the crown. Drawn from each cut's own model.
Face-up size 106 against 100 for the T73 Round Brilliant in peridot (T73 = 100): 6% more face-up area for the same weight
Face-up size is the outline's area per carat, measured from each model (T73 = 100): 106 for the T105 Round Brilliant against 100 for the T73. The same volume spread over a longer or shallower outline shows more face for the weight; it is the same in every stone, because specific gravity scales every cut alike.
T105 Round Brilliant · 6.80 mm at 1.00 ct · Face-up size 106
T73 Round Brilliant · 6.58 mm at 1.00 ct · Face-up size 100
Both stones weigh 1.00 ct in peridot and are drawn to the same scale in millimeters, from each cut's own model. Face-up size is the outline's area per carat, with the T73 at 100: a deeper stone, or a rounder outline, spreads less area for its weight.
0.87 ct at 6.5 mm, against 0.92 ct for the same cut in diamond (−5%)
Weight follows specific gravity: 3.35 for peridot against 3.52 for diamond, so the same model at the same size weighs 0.87 ct here and 0.92 ct in diamond, 6.5 mm across. Nothing about the light changes with it.
A T105 Round Brilliant 6.5 mm across, weighed from the model's measured volume and each stone's specific gravity.
Fire 53 against 77 for the T105 Round Brilliant in diamond: 24 points lower
Fire is the share of the returned light that splits into color at the exit facet: the census traces each exit again at the refractive index minus and plus the fire spread (0.017 in peridot) and counts a ray as fire when the two directions differ by more than 0.6°. The T105 Round Brilliant reads 53 against 77 for the same cut in diamond. The figure is the census's; the 3D Gemstone Simulator renders peridot's fire live.
The fire figure is the census's, traced at the refractive index minus and plus the fire spread. See the fire in the 3D Gemstone Simulator: the T105 Round Brilliant in peridot under the sunny-day lighting.
What helps:the DG-Elongated Hexagon reads 83 for fire in peridot, the best of the cuts we score there.
Leakage 16 against 1 for the T105 Round Brilliant in diamond: 15 points higher
Leakage is the share of the census rays that enter the stone and leave through the pavilion, or through the crown heading down. The T105 Round Brilliant leaks 16% in peridot against 1% for the same cut in diamond. Grey in the maps below is leaking light; the share under each picture is that picture's own.
T105 Round Brilliant in peridot · Leakage 16
0° · 18% leak
10° · 27% leak
20° · 34% leak
30° · 34% leak
T105 Round Brilliant in diamond · Leakage 1
0° · 2% leak
10° · 2% leak
20° · 11% leak
30° · 14% leak
Each frame is the Light Return map with the stone tilted away from you by the angle shown; gray is leakage. The share under each frame is that picture's own.
What helps:the DG-M5 reads 1% for leakage in peridot, the best of the cuts we score there.
Brilliance 84 against 95 for the T105 Round Brilliant in diamond: 11 points lower
The same cut in diamond returns 95. Peridot bends light less than diamond: its critical angle is 37.3°, diamond's 24.4°, so a pavilion facet has to be steeper before light reflects off it rather than passing out. The T105 Round Brilliant's pavilion returns less of peridot's light than of diamond's, as the two maps show.
T105 Round Brilliant in peridot · Brilliance 84
T105 Round Brilliant in diamond · Brilliance 95
Red, green and blue = light returning to the eye; gray = leakage, light that leaves heading down or stays inside. This is the head-on view; the Brilliance score averages a wider cone of light, so the score can differ from what one picture shows.
What helps:the DG-M5 reads 99 for brilliance in peridot, the best of the cuts we score there.
Tilt 77 against 87 for the T105 Round Brilliant in diamond: 10 points lower
Tilt is how much of its face-up brilliance a stone keeps when the census tilts it 20° about its long axis, with 2,200 rays. The T105 Round Brilliant keeps 77 against 87 for the same cut in diamond. The tilt strips below show the maps at 0°, 10°, 20° and 30°, with each picture's own leak share under it.
T105 Round Brilliant in peridot · Tilt 77
0° · 18% leak
10° · 27% leak
20° · 34% leak
30° · 34% leak
T105 Round Brilliant in diamond · Tilt 87
0° · 2% leak
10° · 2% leak
20° · 11% leak
30° · 14% leak
Tilt is how much of its own face-up light a stone keeps when tilted. Each frame is the Light Return map with the stone tilted away from you by the angle shown; gray is leakage. The share under each frame is that picture's own.
What helps:the DG-Miliano reads 84 for tilt in peridot, the best of the cuts we score there.
Our verdict on the T105 Round Brilliant in peridot
Pick the T105 Round Brilliant in peridot for this: it has more facets to sparkle with, faces up larger for its weight and weighs less than in diamond. The catch: it shows less fire than in diamond, leaks more than in diamond, returns less light than in diamond and loses more light when tilted than in diamond.
If that catch matters more to you, the DG-Elongated Hexagon reads 83 for fire in peridot, the best of the cuts we score there.
Every figure on this page is from our light census, traced at one refractive index: a simulation of the geometry, not a grading report. The 3D files and cutting files below are the same T105 Round Brilliant model we traced.
T105 Round Brilliant Peridot: questions
Is the T105 a good cut for peridot?
In our census the T105 Round Brilliant returns 84 of 100 for brilliance and 53 for fire in peridot, against 90 and 53 for the T73 in the same stone. Against that round and against the same cut in diamond it has 3 pros and 4 cons by our thresholds; the summary above names them.
What pavilion angle does peridot need?
At least 37.3° for a round design: peridot's critical angle is 37.3°, from the low end of its refractive index range, and head-on light has to reflect off both sides of the pavilion and leave through the table. The T105 Round Brilliant's pavilion mains sit at 40.8°.
How much does a T105 weigh in peridot?
At 6.5 mm across, 0.87 ct in peridot, against 0.92 ct for the same cut in diamond (-5%): peridot's specific gravity is 3.35, diamond's 3.52.
Can I see the T105 in peridot in 3D?
Yes: the 3D Gemstone Simulator renders it live, with peridot's own refractive index and dispersion. Peridot is traced by the same light census as the other gemstones, with its refractive index and fire spread derived from published values, so its scores are on the same scale; the pictures here are our Light Return tracer, and the Cut Performance Wheel sets it against any other cut and stone.
Get the T105 Round Brilliant Cut files
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T105 Round Brilliant Cut 3D files
The T105 Round Brilliant Cut as exact geometry: 105 planar facets, real-world scale, ready for CAD,
rendering, printing and casting.
