Rectangle Cut Tourmaline: faces up larger for its weight
Brilliance 34 · Fire 61 · Scintillation 63 · in our census, where the T73 scores 86 · 50 · 80 in tourmaline
How the Rectangle Cut handles light in tourmaline, measured: brilliance 34, fire 61 and 62% leakage, set against the T73 in the same stone and against the same cut in diamond.
Light Return map of the Rectangle Cut in tourmaline, face-up, from our own tracer at refractive index 1.603. Red, green and blue return light to the eye; gray leaks.
Rectangle Cut Tourmaline
Tourmaline has a refractive index of 1.603 to 1.655 and a dispersion of 0.017. Its critical angle, from the low end of that range, is 38.6°, so a round design needs a pavilion of at least 38.6° for head-on light to reflect off both sides of the pavilion and leave through the table. We trace it with one index, 1.629, the midpoint of the published range, and a fire spread of 0.015, 0.86 of the published dispersion. Every picture here is our Light Return tracer at 1.603, and every figure is from the same light census that scores the other gemstones; the 3D Gemstone Simulator shows the Rectangle Cut in tourmaline live. Tourmaline is strongly doubly refractive (birefringence up to 0.040), so its back facets can look doubled. Our census traces one index (1.629), so the doubling is not in these figures.
The Rectangle Cut has 45 facets and a total depth of 62.0% of its width; its pavilion mains sit at 33.5°. In tourmaline, the census returns 34 of 100 for brilliance and 61 for fire, against 86 and 50 for the T73, our benchmark, in the same stone; the same Rectangle Cut in diamond reads 50 and 77.
Is tourmaline good in a Rectangle? Pros and cons, measured
Compared with the T73 Round Brilliant in tourmaline and with the Rectangle Cut 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 Rectangle Cut in tourmaline (white) against the T73 Round Brilliant in tourmaline (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 tourmaline: ahead on 2, level on 2, behind on 4.
Global58, the comparison 78, difference −20
Brilliance34, the comparison 86, difference −52
Fire61, the comparison 50, difference +11
Scintillation63, the comparison 80, difference −17
Spread100, the comparison 100, difference 0
Symmetry100, the comparison 100, difference 0
Shape-norm44, the comparison 93, difference −49
Tilt92, the comparison 74, difference +18
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 Rectangle Cut gains in tourmaline
Faces up larger for its weight
Face-up size 121 against 100 for the T73 Round Brilliant in tourmaline (T73 = 100): 21% more face-up area for the same weight
Face-up size is the outline's area per carat, measured from each model (T73 = 100): 121 for the Rectangle Cut 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.
Rectangle Cut · 7.95 x 5.28 mm at 1.00 ct · Face-up size 121
T73 Round Brilliant · 6.74 mm at 1.00 ct · Face-up size 100
Both stones weigh 1.00 ct in tourmaline 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.
1.87 ct at 6.5 mm, against 2.10 ct for the same cut in diamond (−11%)
Weight follows specific gravity: 3.13 for tourmaline against 3.52 for diamond, so the same model at the same size weighs 1.87 ct here and 2.10 ct in diamond, 6.5 mm across. Nothing about the light changes with it.
A Rectangle Cut 6.5 mm across, weighed from the model's measured volume and each stone's specific gravity.
Brilliance 34 against 86 for the T73 Round Brilliant in tourmaline: 52 points lower
Brilliance is the share of the 3,200 census rays that enter the stone and come back out of the crown towards the viewer. In tourmaline, whose critical angle is 38.6°, the Rectangle Cut returns 34 of 100 and the T73 86. The Rectangle Cut's pavilion mains sit at 33.5°, the T73's at 40.8°. The maps below show where each stone's light returns from and where it leaks.
Rectangle Cut in tourmaline · Brilliance 34
T73 Round Brilliant in tourmaline · Brilliance 86
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 96 for brilliance in tourmaline, the best of the cuts we score there.
Leakage 62 against 14 for the T73 Round Brilliant in tourmaline: 48 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 Rectangle Cut leaks 62% in tourmaline against 14% for the T73 in tourmaline. Grey in the maps below is leaking light; the share under each picture is that picture's own.
Rectangle Cut in tourmaline · Leakage 62
0° · 68% leak
10° · 65% leak
20° · 67% leak
30° · 66% leak
T73 Round Brilliant in tourmaline · Leakage 14
0° · 10% leak
10° · 28% leak
20° · 32% leak
30° · 37% 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 4% for leakage in tourmaline, the best of the cuts we score there.
Scintillation 63 against 80 for the T73 Round Brilliant in tourmaline: 17 points lower
Scintillation follows the number of facets the stone shows: 100 × (1 − e^(−facets / 45)). The Rectangle Cut has 45 facets and the T73 73, so 63 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.
What helps:the DG-Miliano reads 98 for scintillation in tourmaline, the best of the cuts we score there.
Fire 61 against 77 for the Rectangle Cut in diamond: 16 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 (0.015 in tourmaline) and counts a ray as fire when the two directions differ by more than 0.6°. The Rectangle Cut reads 61 against 77 for the same cut in diamond. The figure is the census's; the 3D Gemstone Simulator renders tourmaline'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 Rectangle Cut in tourmaline under the sunny-day lighting.
What helps:the Oval Cut reads 80 for fire in tourmaline, the best of the cuts we score there.
Pick the Rectangle Cut in tourmaline for this: it faces up larger for its weight and weighs less than in diamond. The catch: it returns less light than the T73, leaks more light than the T73, has fewer facets to sparkle with and shows less fire than in diamond.
If that catch matters more to you, the DG-M5 reads 96 for brilliance in tourmaline, 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 Rectangle Cut model we traced.
Rectangle Cut Tourmaline: questions
Is the Rectangle a good cut for tourmaline?
In our census the Rectangle Cut returns 34 of 100 for brilliance and 61 for fire in tourmaline, against 86 and 50 for the T73 in the same stone. Against that round and against the same cut in diamond it has 2 pros and 4 cons by our thresholds; the summary above names them.
What pavilion angle does tourmaline need?
At least 38.6° for a round design: tourmaline's critical angle is 38.6°, 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 Rectangle Cut's pavilion mains sit at 33.5°.
How much does a Rectangle weigh in tourmaline?
At 6.5 mm across, 1.87 ct in tourmaline, against 2.10 ct for the same cut in diamond (-11%): tourmaline's specific gravity is 3.13, diamond's 3.52.
Can I see the Rectangle in tourmaline in 3D?
Yes: the 3D Gemstone Simulator renders it live, with tourmaline's own refractive index and dispersion. Tourmaline 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 Rectangle Cut files
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Rectangle Cut 3D files
The Rectangle Cut as exact geometry: 45 planar facets, real-world scale, ready for CAD,
rendering, printing and casting.
