---
title: "Octagon Cut Iolite: Pros, Cons and Scores"
description: "Octagon Cut in iolite: brilliance 64, fire 42, leakage 36%, 1 pro and 4 cons against the T73, from our ray-traced light census."
url: https://digitalgemology.com/gemstones/iolite/octagon
image: https://digitalgemology.com/img/stone-cuts/octagon-iolite-og.jpg?v=60700235
---

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# Octagon Cut Iolite: lighter than the same cut in diamond

**Buy (instant download, personal-use license):** [Octagon Cut 3D files, €9.99 · Personal use](https://digitalgemology.lemonsqueezy.com/checkout/buy/26baac35-16bd-4143-97ba-9eeb7fd4da11) · [Octagon Cut cutting files, €6.99 · Personal use](https://digitalgemology.lemonsqueezy.com/checkout/buy/390b595d-894b-4e34-be35-57f44d569591) · [Buy the bundle](https://digitalgemology.lemonsqueezy.com/checkout/buy/9170b0c0-5357-490e-b6ef-3ce4f7fcd282?checkout%5Bdiscount_code%5D=BUNDLE25) · [Get the cube free](https://digitalgemology.lemonsqueezy.com/checkout/buy/2d1ab55f-2bd6-4897-a4cd-f3320f54e99e)

Brilliance 64 · Fire 42 · Scintillation 66 · in our census, where the T73 scores 72 · 58 · 80 in iolite

How the Octagon Cut handles light in iolite, measured: brilliance 64, fire 42 and 36% leakage, set against the T73 in the same stone and against the same cut in diamond.

[Get the files](https://digitalgemology.com/gemstones/iolite/octagon#buy) [Open it in the Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator?cut=octagon&stone=iolite&ct=1.00&view=angle&lighting=studio&turn=0) [All cuts in iolite](https://digitalgemology.com/gemstones/iolite)

Light Return map of the Octagon Cut in iolite, face-up, from our own tracer at refractive index 1.542. Red, green and blue return light to the eye; gray leaks.

## Octagon Cut Iolite

Iolite has a refractive index of 1.542 to 1.551 and a dispersion of 0.017. Its critical angle, from the low end of that range, is 40.4°, so a round design needs a pavilion of at least 40.4° for head-on light to reflect off both sides of the pavilion and leave through the table. We trace it with one index, 1.547, 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 1.542, and every figure is from the same light census that scores the other gemstones; the 3D Gemstone Simulator shows the Octagon Cut in iolite 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 iolite, the census returns 64 of 100 for brilliance and 42 for fire, against 72 and 58 for the T73, our benchmark, in the same stone; the same Octagon Cut in diamond reads 71 and 76.

## Is iolite good in an Octagon? Pros and cons, measured

### Pros

- [Lighter than the same cut in diamond](https://digitalgemology.com/gemstones/iolite/octagon#pro-weight) 0.91 vs 1.23 ct

### Cons

- [Less fire in iolite than in diamond](https://digitalgemology.com/gemstones/iolite/octagon#con-fire) 42 vs 76
- [Leaks more in iolite than in diamond](https://digitalgemology.com/gemstones/iolite/octagon#con-leak) 36 vs 18
- [Loses more light when tilted than in diamond](https://digitalgemology.com/gemstones/iolite/octagon#con-tiltStab) 83 vs 97
- [Fewer facets, less sparkle](https://digitalgemology.com/gemstones/iolite/octagon#con-scint) 66 vs 80

Compared with the T73 Round Brilliant in iolite 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](https://digitalgemology.com/about/how-we-measure).

## All eight scores against the T73

At a glance: the Octagon Cut in iolite (white) against the T73 Round Brilliant in iolite (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 iolite: ahead on 2, level on 2, behind on 4.

- Global 67, the comparison 74, difference −7
- Brilliance 64, the comparison 72, difference −8
- Fire 42, the comparison 58, difference −16
- Scintillation 66, the comparison 80, difference −14
- Spread 100, the comparison 100, difference 0
- Symmetry 100, the comparison 100, difference 0
- Shape-norm 84, the comparison 77, difference +7
- Tilt 83, the comparison 81, difference +2

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](https://digitalgemology.com/tools/cut-performance-wheel?cut=octagon&stone=iolite); these are the same census figures as our [Cut Performance Index](https://digitalgemology.com/learn/cut-performance-index).

## What the Octagon Cut gains in iolite

### Lighter than the same cut in diamond

**0.91 ct** at 6.5 mm, against 1.23 ct for the same cut in diamond (−26%)

Weight follows specific gravity: 2.61 for iolite against 3.52 for diamond, so the same model at the same size weighs 0.91 ct here and 1.23 ct in diamond, 6.5 mm across. Nothing about the light changes with it.

*Weight of a 6.5 mm Octagon Cut: 0.91 ct in iolite, 1.23 ct in diamond*

A Octagon Cut 6.5 mm across, weighed from the model's measured volume and each stone's specific gravity.

[Try it yourself: Weights in every gemstone on the Octagon Cut page](https://digitalgemology.com/cuts/octagon#stones)

## What the Octagon Cut gives up in iolite

### Less fire in iolite than in diamond

**Fire 42** against 76 for the Octagon Cut in diamond: 34 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 iolite) and counts a ray as fire when the two directions differ by more than 0.6°. The Octagon Cut reads 42 against 76 for the same cut in diamond. The figure is the census's; the 3D Gemstone Simulator renders iolite'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](https://digitalgemology.com/tools/3d_gemstone_simulator?cut=octagon&stone=iolite&ct=1.00&view=up&lighting=sun&turn=0): the Octagon Cut in iolite under the sunny-day lighting.

**What helps:** [the Oval Cut](https://digitalgemology.com/gemstones/iolite/oval) reads 82 for fire in iolite, the best of the cuts we score there.

[Try it yourself: See the fire in the 3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator?cut=octagon&stone=iolite&ct=1.00&view=up&lighting=sun&turn=0)

### Leaks more in iolite than in diamond

**Leakage 36** against 18 for the Octagon Cut in diamond: 18 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 36% in iolite 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 iolite · Leakage 36

0° · 21% leak

10° · 41% leak

20° · 39% leak

30° · 42% leak

Octagon Cut in diamond · Leakage 18

0° · 23% leak

10° · 15% leak

20° · 19% leak

30° · 23% 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](https://digitalgemology.com/gemstones/iolite/dg-m5) reads 15% for leakage in iolite, the best of the cuts we score there.

[Try it yourself: Tilt it yourself in the simulator's light map](https://digitalgemology.com/tools/3d_gemstone_simulator?cut=octagon&stone=iolite&ct=1.00&view=up&map=1&turn=0)

### Loses more light when tilted than in diamond

**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 iolite · Tilt 83

0° · 21% leak

10° · 41% leak

20° · 39% leak

30° · 42% leak

Octagon Cut in diamond · Tilt 97

0° · 23% leak

10° · 15% leak

20° · 19% leak

30° · 23% 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 T105 Round Brilliant](https://digitalgemology.com/gemstones/iolite/t105-round-brilliant) reads 87 for tilt in iolite, the best of the cuts we score there.

[Try it yourself: Compare the Tilt spoke in the Cut Performance Wheel](https://digitalgemology.com/tools/cut-performance-wheel?cut=octagon&stone=iolite&vs=octagon&vsstone=diamond)

### Fewer facets, less sparkle

**Scintillation 66** against 80 for the T73 Round Brilliant in iolite: 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.

*Facet diagram of the Octagon Cut: its crown, seen face-up, 49 facets in all*

Octagon Cut · 49 facets · Scintillation 66

*Facet diagram of the T73 Round Brilliant: its crown, seen face-up, 73 facets in all*

T73 Round Brilliant · 73 facets · Scintillation 80

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](https://digitalgemology.com/gemstones/iolite/dg-miliano) reads 98 for scintillation in iolite, the best of the cuts we score there.

[Try it yourself: Compare the Scintillation spoke in the Cut Performance Wheel](https://digitalgemology.com/tools/cut-performance-wheel?cut=octagon&stone=iolite)

## Our verdict on the Octagon Cut in iolite

Pick the Octagon Cut in iolite for this: it weighs less than in diamond. The catch: it shows less fire than in diamond, leaks more than in diamond, loses more light when tilted than in diamond and has fewer facets to sparkle with.

If that catch matters more to you, [the Oval Cut](https://digitalgemology.com/gemstones/iolite/oval) reads 82 for fire in iolite, 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.

## Octagon Cut Iolite: questions

### Is the Octagon a good cut for iolite?

In our census the Octagon Cut returns 64 of 100 for brilliance and 42 for fire in iolite, against 72 and 58 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.

### What pavilion angle does iolite need?

At least 40.4° for a round design: iolite's critical angle is 40.4°, 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°.

### How much does a Octagon weigh in iolite?

At 6.5 mm across, 0.91 ct in iolite, against 1.23 ct for the same cut in diamond (-26%): iolite's specific gravity is 2.61, diamond's 3.52.

### Can I see the Octagon in iolite in 3D?

Yes: the 3D Gemstone Simulator renders it live, with iolite's own refractive index and dispersion. Iolite 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 Octagon Cut files

*6 formats* *Millimeters* *Watertight*

### Octagon Cut 3D files

The Octagon Cut as exact geometry: 49 planar facets, real-world scale, ready for CAD, rendering, printing and casting.

- **STEP** Exact faceted solid for CAD
- **3DM** Rhino, closed mesh on its own layer
- **STL** Watertight mesh for printing and casting
- **OBJ** Mesh for modeling and rendering
- **FBX** Blender, 3ds Max, Maya, Cinema 4D, Unity, Unreal
- **GLB** Web, AR and quick previews

€9.99 · [Personal use](https://digitalgemology.com/licence) [Buy the 3D files](https://digitalgemology.lemonsqueezy.com/checkout/buy/26baac35-16bd-4143-97ba-9eeb7fd4da11)

*GemCad* *96 index*

### Octagon Cut cutting files

The Octagon Cut as a faceting design: 41 + 8 girdles = 49 facets, 96 index, 8-fold mirror-image symmetry, ready for the machine.

- **.asc** GemCad design file, 96 index gear
- **.csv** Tier table: angles, indices and cutting order
- **Diagram** Printable faceting diagram

€6.99 · [Personal use](https://digitalgemology.com/licence) [Buy the cutting files](https://digitalgemology.lemonsqueezy.com/checkout/buy/390b595d-894b-4e34-be35-57f44d569591)

Save with a bundle: the Octagon Cut cutting files are also in [Faceter's Classics](https://digitalgemology.com/cuts/#bundles), 10 cuts for €22.49 until 1 December, then €29.99 (€69.90 as single files). [Buy the bundle](https://digitalgemology.lemonsqueezy.com/checkout/buy/9170b0c0-5357-490e-b6ef-3ce4f7fcd282?checkout%5Bdiscount_code%5D=BUNDLE25).

Not sure the files open in your software? [Get the cube free](https://digitalgemology.lemonsqueezy.com/checkout/buy/2d1ab55f-2bd6-4897-a4cd-f3320f54e99e): the same six formats, for your email address, used only to send them ([privacy](https://digitalgemology.com/privacy#free-sample)).

Questions before you buy? [Email us](mailto:support@digitalgemology.com).

## More gemstones and cuts

[Iolite: optical properties and the top ten cuts](https://digitalgemology.com/gemstones/iolite) · [The Octagon Cut: specifications, model and files](https://digitalgemology.com/cuts/octagon)

### Other cuts in iolite

- [T73 Round Brilliant](https://digitalgemology.com/gemstones/iolite/t73-round-brilliant)
- [T105 Round Brilliant](https://digitalgemology.com/gemstones/iolite/t105-round-brilliant)
- [DG-Vitruvio](https://digitalgemology.com/gemstones/iolite/dg-vitruvio)
- [DG-Anteros](https://digitalgemology.com/gemstones/iolite/dg-anteros)
- [DG-Broken Hearts and Arrows](https://digitalgemology.com/gemstones/iolite/dg-broken-hearts-and-arrows)
- [Baguette Cut](https://digitalgemology.com/gemstones/iolite/baguette)
- [Emerald Cut](https://digitalgemology.com/gemstones/iolite/emerald-cut)
- [Marquise Cut](https://digitalgemology.com/gemstones/iolite/marquise)
- [Oval Cut](https://digitalgemology.com/gemstones/iolite/oval)
- [Pear Cut](https://digitalgemology.com/gemstones/iolite/pear)
- [Radiant Cut](https://digitalgemology.com/gemstones/iolite/radiant)
- [Rectangle Cut](https://digitalgemology.com/gemstones/iolite/rectangle)
- [Teardrop Cut](https://digitalgemology.com/gemstones/iolite/teardrop)
- [Asscher Cut](https://digitalgemology.com/gemstones/iolite/asscher)
- [Cushion Cut](https://digitalgemology.com/gemstones/iolite/cushion)
- [Emerald Square Cut](https://digitalgemology.com/gemstones/iolite/emerald-square)
- [Princess Cut](https://digitalgemology.com/gemstones/iolite/princess)
- [Radiant Square Cut](https://digitalgemology.com/gemstones/iolite/radiant-square)
- [Square Cut](https://digitalgemology.com/gemstones/iolite/square)
- [Triangle Cut](https://digitalgemology.com/gemstones/iolite/triangle)
- [Trilliant Cut](https://digitalgemology.com/gemstones/iolite/trilliant)
- [Trillion Cut](https://digitalgemology.com/gemstones/iolite/trillion)
- [Hexagon Cut](https://digitalgemology.com/gemstones/iolite/hexagon)
- [Portuguese Bird's Nest Cut](https://digitalgemology.com/gemstones/iolite/portuguese-birds-nest)
- [Old Single Cut](https://digitalgemology.com/gemstones/iolite/old-single)
- [Mazarin Cut](https://digitalgemology.com/gemstones/iolite/mazarin)
- [Peruzzi Cut](https://digitalgemology.com/gemstones/iolite/peruzzi)
- [Old Mine Cut](https://digitalgemology.com/gemstones/iolite/old-mine)
- [Old European Cut](https://digitalgemology.com/gemstones/iolite/old-european)
- [T57 Round Brilliant](https://digitalgemology.com/gemstones/iolite/t57-round-brilliant)
- [DG-M5](https://digitalgemology.com/gemstones/iolite/dg-m5)
- [DG-Miliano](https://digitalgemology.com/gemstones/iolite/dg-miliano)
- [DG-Rafaello](https://digitalgemology.com/gemstones/iolite/dg-rafaello)
- [DG-Bowtie](https://digitalgemology.com/gemstones/iolite/dg-bowtie)
- [DG-Elongated Hexagon](https://digitalgemology.com/gemstones/iolite/dg-elongated-hexagon)
- [DG-Octagonal Kite](https://digitalgemology.com/gemstones/iolite/dg-octagonal-kite)

### The Octagon Cut in other gemstones

- [Moissanite](https://digitalgemology.com/gemstones/moissanite/octagon)
- [Diamond](https://digitalgemology.com/gemstones/diamond/octagon)
- [Cubic Zirconia](https://digitalgemology.com/gemstones/cubic-zirconia/octagon)
- [Ruby](https://digitalgemology.com/gemstones/ruby/octagon)
- [Sapphire](https://digitalgemology.com/gemstones/sapphire/octagon)
- [Emerald](https://digitalgemology.com/gemstones/emerald/octagon)
- [Amethyst](https://digitalgemology.com/gemstones/amethyst/octagon)
- [Topaz](https://digitalgemology.com/gemstones/topaz/octagon)
- [Spinel](https://digitalgemology.com/gemstones/spinel/octagon)
- [Demantoid](https://digitalgemology.com/gemstones/demantoid/octagon)
- [Zircon](https://digitalgemology.com/gemstones/zircon/octagon)
- [Tourmaline](https://digitalgemology.com/gemstones/tourmaline/octagon)
- [Peridot](https://digitalgemology.com/gemstones/peridot/octagon)
- [Tanzanite](https://digitalgemology.com/gemstones/tanzanite/octagon)
- [YAG](https://digitalgemology.com/gemstones/yag/octagon)
- [Pyrope](https://digitalgemology.com/gemstones/pyrope/octagon)
- [Almandine](https://digitalgemology.com/gemstones/almandine/octagon)
- [Spessartine](https://digitalgemology.com/gemstones/spessartine/octagon)
- [Grossular](https://digitalgemology.com/gemstones/grossular/octagon)
- [Chrysoberyl](https://digitalgemology.com/gemstones/chrysoberyl/octagon)
- [Kunzite](https://digitalgemology.com/gemstones/kunzite/octagon)
- [Morganite](https://digitalgemology.com/gemstones/morganite/octagon)
- [GGG](https://digitalgemology.com/gemstones/ggg/octagon)
- [Strontium titanate](https://digitalgemology.com/gemstones/strontium-titanate/octagon)
- [Synthetic rutile](https://digitalgemology.com/gemstones/synthetic-rutile/octagon)