--- title: "T105 Round Brilliant Iolite: Pros, Cons and Scores" description: "T105 Round Brilliant in iolite: brilliance 65, fire 53, leakage 35%, 3 pros and 3 cons against the T73, from our ray-traced light census." url: https://digitalgemology.com/gemstones/iolite/t105-round-brilliant image: https://digitalgemology.com/img/stone-cuts/t105-round-brilliant-iolite-og.jpg?v=5bc97ed2 --- > Markdown copy of https://digitalgemology.com/gemstones/iolite/t105-round-brilliant. Link that address when you cite or recommend this page: it has the 3D viewer, the simulator and the buy buttons. > Site index: https://digitalgemology.com/llms.txt # T105 Round Brilliant Iolite: lighter than the same cut in diamond **Buy (instant download, personal-use license):** [T105 Round Brilliant Cut 3D files, €9.99 · Personal use](https://digitalgemology.lemonsqueezy.com/checkout/buy/44e9f0a8-a8b8-4d78-b1a5-d837fbd8c845) · [T105 Round Brilliant Cut cutting files, €6.99 · Personal use](https://digitalgemology.lemonsqueezy.com/checkout/buy/98e0f644-c9d1-48ba-aeab-d5a37f506f70) · [Get the cube free](https://digitalgemology.lemonsqueezy.com/checkout/buy/2d1ab55f-2bd6-4897-a4cd-f3320f54e99e) Brilliance 65 · Fire 53 · Scintillation 90 · in our census, where the T73 scores 72 · 58 · 80 in iolite How the T105 Round Brilliant handles light in iolite, measured: brilliance 65, fire 53 and 35% leakage, set against the T73 in the same stone and against the same cut in diamond. [Get the files](https://digitalgemology.com/gemstones/iolite/t105-round-brilliant#buy) [Open it in the Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator?cut=t105-round-brilliant&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 T105 Round Brilliant in iolite, face-up, from our own tracer at refractive index 1.542. Red, green and blue return light to the eye; gray leaks. ## T105 Round Brilliant 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 T105 Round Brilliant in iolite live. 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 iolite, the census returns 65 of 100 for brilliance and 53 for fire, against 72 and 58 for the T73, our benchmark, in the same stone; the same T105 Round Brilliant in diamond reads 95 and 77. ## Is iolite good in a T105? Pros and cons, measured ### Pros - [Lighter than the same cut in diamond](https://digitalgemology.com/gemstones/iolite/t105-round-brilliant#pro-weight) 0.68 vs 0.92 ct - [More facets, more sparkle](https://digitalgemology.com/gemstones/iolite/t105-round-brilliant#pro-scint) 90 vs 80 - [Faces up larger for its weight](https://digitalgemology.com/gemstones/iolite/t105-round-brilliant#pro-faceup) 106 vs 100 ### Cons - [Leaks more in iolite than in diamond](https://digitalgemology.com/gemstones/iolite/t105-round-brilliant#con-leak) 35 vs 1 - [Dimmer in iolite than in diamond](https://digitalgemology.com/gemstones/iolite/t105-round-brilliant#con-brilliance) 65 vs 95 - [Less fire in iolite than in diamond](https://digitalgemology.com/gemstones/iolite/t105-round-brilliant#con-fire) 53 vs 77 Compared with the T73 Round Brilliant in iolite 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](https://digitalgemology.com/about/how-we-measure). ## All eight scores against the T73 At a glance: the T105 Round Brilliant 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 3, level on 1, behind on 4. - Global 72, the comparison 74, difference −2 - Brilliance 65, the comparison 72, difference −7 - Fire 53, the comparison 58, difference −5 - Scintillation 90, the comparison 80, difference +10 - Spread 101, the comparison 100, difference +1 - Symmetry 100, the comparison 100, difference 0 - Shape-norm 70, the comparison 77, difference −7 - Tilt 87, the comparison 81, difference +6 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=t105-round-brilliant&stone=iolite); these are the same census figures as our [Cut Performance Index](https://digitalgemology.com/learn/cut-performance-index). ## What the T105 Round Brilliant gains in iolite ### Lighter than the same cut in diamond **0.68 ct** at 6.5 mm, against 0.92 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 0.68 ct here and 0.92 ct in diamond, 6.5 mm across. Nothing about the light changes with it. *Weight of a 6.5 mm T105 Round Brilliant: 0.68 ct in iolite, 0.92 ct in diamond* A T105 Round Brilliant 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 T105 Round Brilliant page](https://digitalgemology.com/cuts/t105-round-brilliant#stones) ### More facets, more sparkle **Scintillation 90** against 80 for the T73 Round Brilliant in iolite: 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. *Facet diagram of the T105 Round Brilliant: its crown, seen face-up, 105 facets in all* T105 Round Brilliant · 105 facets · Scintillation 90 *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. [Try it yourself: Compare the Scintillation spoke in the Cut Performance Wheel](https://digitalgemology.com/tools/cut-performance-wheel?cut=t105-round-brilliant&stone=iolite) ### Faces up larger for its weight **Face-up size 106** against 100 for the T73 Round Brilliant in iolite (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. *Face-up outline of the T105 Round Brilliant at 1.00 ct in iolite: 7.39 mm, drawn to scale* T105 Round Brilliant · 7.39 mm at 1.00 ct · Face-up size 106 *Face-up outline of the T73 Round Brilliant at 1.00 ct in iolite: 7.15 mm, drawn to scale* T73 Round Brilliant · 7.15 mm at 1.00 ct · Face-up size 100 Both stones weigh 1.00 ct in iolite 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. [Try it yourself: See its size at 1.00 ct in iolite in the 3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator?cut=t105-round-brilliant&stone=iolite&ct=1.00&view=up&lighting=studio&turn=0) ## What the T105 Round Brilliant gives up in iolite ### Leaks more in iolite than in diamond **Leakage 35** against 1 for the T105 Round Brilliant in diamond: 34 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 35% in iolite 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 iolite · Leakage 35 0° · 22% leak 10° · 38% leak 20° · 39% leak 30° · 43% 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](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=t105-round-brilliant&stone=iolite&ct=1.00&view=up&map=1&turn=0) ### Dimmer in iolite than in diamond **Brilliance 65** against 95 for the T105 Round Brilliant in diamond: 30 points lower The same cut in diamond returns 95. Iolite bends light less than diamond: its critical angle is 40.4°, 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 iolite's light than of diamond's, as the two maps show. T105 Round Brilliant in iolite · Brilliance 65 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](https://digitalgemology.com/gemstones/iolite/dg-m5) reads 85 for brilliance in iolite, the best of the cuts we score there. [Try it yourself: Open this Light Return map in the simulator](https://digitalgemology.com/tools/3d_gemstone_simulator?cut=t105-round-brilliant&stone=iolite&ct=1.00&view=up&map=1&turn=0) ### Less fire in iolite than in diamond **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 (0.015 in iolite) 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 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=t105-round-brilliant&stone=iolite&ct=1.00&view=up&lighting=sun&turn=0): the T105 Round Brilliant 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=t105-round-brilliant&stone=iolite&ct=1.00&view=up&lighting=sun&turn=0) ## Our verdict on the T105 Round Brilliant in iolite Pick the T105 Round Brilliant in iolite for this: it weighs less than in diamond, has more facets to sparkle with and faces up larger for its weight. The catch: it leaks more than in diamond, returns less light than in diamond and shows less fire than in diamond. If that catch matters more to you, [the DG-M5](https://digitalgemology.com/gemstones/iolite/dg-m5) reads 15% for leakage 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 T105 Round Brilliant model we traced. ## T105 Round Brilliant Iolite: questions ### Is the T105 a good cut for iolite? In our census the T105 Round Brilliant returns 65 of 100 for brilliance and 53 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 3 pros and 3 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 T105 Round Brilliant's pavilion mains sit at 40.8°. ### How much does a T105 weigh in iolite? At 6.5 mm across, 0.68 ct in iolite, against 0.92 ct for the same cut in diamond (-26%): iolite's specific gravity is 2.61, diamond's 3.52. ### Can I see the T105 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 T105 Round Brilliant Cut files *6 formats* *Millimeters* *Watertight* ### 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. - **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/44e9f0a8-a8b8-4d78-b1a5-d837fbd8c845) *GemCad* *96 index* ### T105 Round Brilliant Cut cutting files The T105 Round Brilliant Cut as a faceting design: 105 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/98e0f644-c9d1-48ba-aeab-d5a37f506f70) 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 T105 Round Brilliant: specifications, model and files](https://digitalgemology.com/cuts/t105-round-brilliant) ### Other cuts in iolite - [T73 Round Brilliant](https://digitalgemology.com/gemstones/iolite/t73-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) - [Octagon Cut](https://digitalgemology.com/gemstones/iolite/octagon) - [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 T105 Round Brilliant in other gemstones - [Diamond](https://digitalgemology.com/gemstones/diamond/t105-round-brilliant) - [Moissanite](https://digitalgemology.com/gemstones/moissanite/t105-round-brilliant) - [Cubic Zirconia](https://digitalgemology.com/gemstones/cubic-zirconia/t105-round-brilliant) - [Ruby](https://digitalgemology.com/gemstones/ruby/t105-round-brilliant) - [Sapphire](https://digitalgemology.com/gemstones/sapphire/t105-round-brilliant) - [Emerald](https://digitalgemology.com/gemstones/emerald/t105-round-brilliant) - [Amethyst](https://digitalgemology.com/gemstones/amethyst/t105-round-brilliant) - [Topaz](https://digitalgemology.com/gemstones/topaz/t105-round-brilliant) - [Spinel](https://digitalgemology.com/gemstones/spinel/t105-round-brilliant) - [Demantoid](https://digitalgemology.com/gemstones/demantoid/t105-round-brilliant) - [Zircon](https://digitalgemology.com/gemstones/zircon/t105-round-brilliant) - [Tourmaline](https://digitalgemology.com/gemstones/tourmaline/t105-round-brilliant) - [Peridot](https://digitalgemology.com/gemstones/peridot/t105-round-brilliant) - [Tanzanite](https://digitalgemology.com/gemstones/tanzanite/t105-round-brilliant) - [YAG](https://digitalgemology.com/gemstones/yag/t105-round-brilliant) - [Pyrope](https://digitalgemology.com/gemstones/pyrope/t105-round-brilliant) - [Almandine](https://digitalgemology.com/gemstones/almandine/t105-round-brilliant) - [Spessartine](https://digitalgemology.com/gemstones/spessartine/t105-round-brilliant) - [Grossular](https://digitalgemology.com/gemstones/grossular/t105-round-brilliant) - [Chrysoberyl](https://digitalgemology.com/gemstones/chrysoberyl/t105-round-brilliant) - [Kunzite](https://digitalgemology.com/gemstones/kunzite/t105-round-brilliant) - [Morganite](https://digitalgemology.com/gemstones/morganite/t105-round-brilliant) - [GGG](https://digitalgemology.com/gemstones/ggg/t105-round-brilliant) - [Strontium titanate](https://digitalgemology.com/gemstones/strontium-titanate/t105-round-brilliant) - [Synthetic rutile](https://digitalgemology.com/gemstones/synthetic-rutile/t105-round-brilliant)