Brilliance 70 · Fire 35 · Scintillation 66 · in our census, where the T73 scores 79 · 39 · 80 in morganite
How the Octagon Cut handles light in morganite, measured: brilliance 70, fire 35 and 30% leakage, set against the T73 in the same stone and against the same cut in diamond.
Morganite has a refractive index of 1.572 to 1.600 and a dispersion of 0.014. Its critical angle, from the low end of that range, is 39.5°, so a round design needs a pavilion of at least 39.5° for head-on light to reflect off both sides of the pavilion and leave through the table. We trace it with one index, 1.586, the midpoint of the published range, and a fire spread of 0.012, 0.86 of the published dispersion. Every picture here is our Light Return tracer at 1.572, and every figure is from the same light census that scores the other gemstones; the 3D Gemstone Simulator shows the Octagon Cut in morganite live.
The Octagon Cut has 49 facets, a table of 60.0% of its width and a total depth of 61.0% of its width; its pavilion mains sit at 29.3°. In morganite, the census returns 70 of 100 for brilliance and 35 for fire, against 79 and 39 for the T73, our benchmark, in the same stone; the same Octagon Cut in diamond reads 71 and 76.
Compared with the T73 Round Brilliant in morganite and with the Octagon 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.
At a glance: the Octagon Cut in morganite (white) against the T73 Round Brilliant in morganite (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 morganite: ahead on 2, level on 2, behind on 4.
1.00 ct at 6.5 mm, against 1.23 ct for the same cut in diamond (−19%)
Weight follows specific gravity: 2.855 for morganite against 3.52 for diamond, so the same model at the same size weighs 1.00 ct here and 1.23 ct in diamond, 6.5 mm across. Nothing about the light changes with it.
Try it yourself: Weights in every gemstone on the Octagon Cut page
Fire 35 against 76 for the Octagon Cut in diamond: 41 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 (0.012 in morganite) and counts a ray as fire when the two directions differ by more than 0.6°. The Octagon Cut reads 35 against 76 for the same cut in diamond. The figure is the census's; the 3D Gemstone Simulator renders morganite'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 Octagon Cut in morganite under the sunny-day lighting.
What helps: the Oval Cut reads 70 for fire in morganite, the best of the cuts we score there.
Tilt 83 against 97 for the Octagon Cut in diamond: 14 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 Octagon Cut keeps 83 against 97 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.
Octagon Cut in morganite · Tilt 83
Octagon Cut in diamond · Tilt 97
What helps: the Square Cut reads 85 for tilt in morganite, the best of the cuts we score there.
Try it yourself: Compare the Tilt spoke in the Cut Performance Wheel
Scintillation 66 against 80 for the T73 Round Brilliant in morganite: 14 points lower
Scintillation follows the number of facets the stone shows: 100 × (1 − e^(−facets / 45)). The Octagon Cut has 49 facets and the T73 73, so 66 against 80. It depends on the geometry alone, so it is the same in every stone.
Octagon Cut · 49 facets · Scintillation 66
T73 Round Brilliant · 73 facets · Scintillation 80
What helps: the DG-Miliano reads 98 for scintillation in morganite, the best of the cuts we score there.
Try it yourself: Compare the Scintillation spoke in the Cut Performance Wheel
Leakage 30 against 18 for the Octagon Cut in diamond: 12 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 Octagon Cut leaks 30% in morganite against 18% for the same cut in diamond. Grey in the maps below is leaking light; the share under each picture is that picture's own.
Octagon Cut in morganite · Leakage 30
Octagon Cut in diamond · Leakage 18
What helps: the DG-M5 reads 9% for leakage in morganite, the best of the cuts we score there.
Try it yourself: Tilt it yourself in the simulator's light map
Pick the Octagon Cut in morganite for this: it weighs less than in diamond. The catch: it shows less fire than in diamond, loses more light when tilted than in diamond, has fewer facets to sparkle with and leaks more than in diamond.
If that catch matters more to you, the Oval Cut reads 70 for fire in morganite, 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 Octagon Cut model we traced.
In our census the Octagon Cut returns 70 of 100 for brilliance and 35 for fire in morganite, against 79 and 39 for the T73 in the same stone. Against that round and against the same cut in diamond it has 1 pro and 4 cons by our thresholds; the summary above names them.
At least 39.5° for a round design: morganite's critical angle is 39.5°, 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 Octagon Cut's pavilion mains sit at 29.3°.
At 6.5 mm across, 1.00 ct in morganite, against 1.23 ct for the same cut in diamond (-19%): morganite's specific gravity is 2.855, diamond's 3.52.
Yes: the 3D Gemstone Simulator renders it live, with morganite's own refractive index and dispersion. Morganite 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.
The Octagon Cut as exact geometry: 49 planar facets, real-world scale, ready for CAD, rendering, printing and casting.
The Octagon Cut as a faceting design: 41 + 8 girdles = 49 facets, 96 index, 8-fold mirror-image symmetry, ready for the machine.
Save with a bundle: the Octagon Cut cutting files are also in Faceter's Classics, 10 cuts for €22.49 until 1 December, then €29.99 (€69.90 as single files). Buy the bundle.
Not sure the files open in your software? Get the cube free: the same six formats, for your email address, used only to send them (privacy).
Questions before you buy? Email us.
Morganite: optical properties and the top ten cuts · The Octagon Cut: specifications, model and files