Cut registry › Jewellery cuts › Trilliant
Jewellery cuts · Fancy brilliant
Not quite a trillion.
Trilliant and trillion are used as synonyms and are not the same stone. On one protocol the difference is clear, and it runs the opposite way to what the names suggest.
The short version
A trilliant cut diamond is a triangular brilliant carrying 70 facets on our measurement, with a shallower outline and a more even face than the trillion it is usually confused with.
The two words are used interchangeably across the trade. The stones behind them are not interchangeable.
Definition
Both names describe a triangular brilliant, and no standard assigns either word to a specific geometry. In practice the trade uses trilliant more often for the deeper, more conventionally faceted stone and trillion for the shallower spread cut, but you cannot rely on it.
What you can do is ask for the facet count and the depth. Our trilliant reference carries 70 facets at 58.9% depth; our trillion reference carries 73 at a considerably shallower profile. Those are different stones regardless of what either is called.
As with any pointed shape, the three corners are the vulnerability. Modern examples are bruted or slightly rounded rather than finished as knife edges, and they still want prongs that cover them.
Proportions
Trade description on the left, our measured reference stone on the right. The depth figure is the clearest difference from the trillion.
| Measure | Commonly cited | Our reference stone | What it does |
|---|---|---|---|
| Outline | triangular, convex sides | triangular | Softly curved rather than straight. |
| Length-to-width | 1.00 to 1.10 | 1.00 | Close to equilateral. |
| Depth | varies widely | 58.9% | Deeper than a trillion, and it returns more light for it. |
| Table | not standardised | 57.5% | The flat top, as a share of the width. |
| Pavilion angle | not commonly published | 40.5° | Close to the modern round brilliant’s. |
| Facets | 31 or 50 commonly cited | 70 | Counted as facets that actually reach the surface. |
No laboratory issues a cut grade for a triangular brilliant, and neither name is standardised. If a supplier quotes you a price on the word alone, ask for the depth and the facet count before you compare it with anything.
Light
Measured on the census that runs on every cut on this site: 3,200 rays face-up, 2,200 at 20° tilt, on exact facet geometry, against T57 as the standard.
| Material | Useful light | Leak | Fire | Scintillation | Global | vs the standard |
|---|---|---|---|---|---|---|
| Diamond | 78.04% | 11.05% | 83.37 | 78.89 | 80.48 | −8.12 |
| Moissanite | 70.98% | 10.67% | 94.72 | 78.89 | 80.49 | −9.33 |
| Cubic zirconia | 83.57% | 11.48% | 94.13 | 78.89 | 84.18 | −7.59 |
| T57 standard, diamond | 92.28% | 1.88% | 78.85 | 71.82 | 88.61 | 0.00 |
The trilliant returns 78.04% of entering light usefully and leaks 11.05%, for 80.48 Global against the standard’s 88.61, which places it fourth of the twenty-one jewellery cuts we publish.
Against the trillion it wins on light and loses on colour. 78.04% of useful light against the trillion’s 66.74%, a large margin, while fire falls to 83.37 against the trillion’s 87.32. The two land within half a point of each other on Global by taking opposite routes, which is exactly why the names being interchangeable is a problem.
Its face is unusually even. Across five bands the trilliant varies by only 2.3 points, against the round-brilliant control’s 1.0, so it has no dark corner and no dark centre.
It carries 70 active facets for 78.89 on scintillation against the standard’s 71.82, and holds 89.43 under tilt against 90.41.
Where the light is: useful return across the face
Five equal bands across the stone, every returning ray binned by where it leaves the crown. The trilliant varies by 2.3 points from centre to edge, which is close to the round-brilliant control’s 1.0 and far flatter than most of the fancy shapes here.
Against the standard
Light return. 78.04% against the standard’s 92.28%, a Global gap of 8.12 points.
Against the trillion. 78.04% of useful light against 66.74%, and 83.37 of fire against 87.32. More light, less colour.
Evenness. 2.3 points across the face against the control’s 1.0. No dark corners, which is unusual for a pointed shape.
Durability. Three corners against a round’s none. Bruted tips and covering prongs are the answer.
Face-up size. 101.46 on the spread axis, above the standard, from a shallow profile.
The baseline for all of this is the round brilliant itself. Its facet plan is set out in the anatomy of a round brilliant, and the measured standard we compare against is T57, the stone Tolkowsky published in 1919.
Materials
In moissanite the trilliant returns 70.98% for 80.49 Global with fire at 94.72.
In cubic zirconia it returns 83.57% for 84.18 Global.
Set it against the trillion in the Index to see the two side by side.
Trade-offs
Questions
The questions buyers actually ask, answered in full. Where the answer is ours to prove, the figure is measured on the Index; where it is an established gemological fact, it is stated as one.
A trilliant cut diamond is a triangular brilliant, carrying 70 facets on our measurement. The name is used interchangeably with trillion across the trade, although the two usually describe stones cut to noticeably different depths.
Neither word is standardised, so the honest answer is that the names do not reliably tell you. The stones can differ a great deal: our trilliant reference returns 78.04% of entering light against our trillion reference’s 66.74%, while the trillion throws more fire, 87.32 against 83.37. Ask for depth and facet count rather than relying on the word.
They finish within half a point of each other on Global, 80.48 against 80.86, by opposite routes. The trilliant returns substantially more light; the trillion throws substantially more colour and spreads a little further. Choose on which of those you want.
Commonly quoted as 31 or 50 depending on whether it is cut as an accent or a centre stone. Our reference trilliant measures 70 facets reaching the surface, which is the count behind its scintillation figure of 78.89.
The three corners are the weak points, as on any pointed shape. Modern trilliants are bruted or slightly rounded at the tips rather than finished as knife edges, and they still need prongs that cover each corner rather than sitting beside it.
Yes, and it makes a better case for it than most triangular cuts. It returns 78.04% of entering light for 80.48 Global, fourth of the twenty-one jewellery cuts we publish, and its face is unusually even at 2.3 points from centre to edge.
Somewhat. It reads 101.46 on the Index spread axis, above the round-brilliant standard, because it is cut shallower than a brilliant. That axis is derived from depth, so it is a claim about millimetres per carat rather than outline area.
No. GIA issues cut grades for round brilliants only. A trilliant report will record colour, clarity, carat, symmetry and polish, and will usually describe the shape as a triangular brilliant or modified brilliant.
Next
See the whole set on the jewellery cuts index, or the measured house and historic cuts in the cut registry.
Method
Monte-Carlo on exact facet geometry: 3,200 rays face-up plus 2,200 at 20° tilt, cosine-weighted from a 7° near-vertical cone. Useful light is what exits through the crown within 64° of vertical. The same protocol runs on every cut on this site, so the figures are comparable to each other.
They measure our reference geometry for the shape at the proportions listed above, not an average of stones on the market. A trilliant cut to different proportions will read differently. Treat them as a like-for-like comparison between shapes, not as a grade for any individual stone.
Engine estimates, ±2 points, not lab-certified grades. We do not publish the Index symmetry axis on these pages: it scores facet regularity within each pavilion family, which is meaningful for a round brilliant and misleading for a shape whose pavilion is deliberately irregular.
78.89 here against the standard’s 71.82. The term is 100(1−e−n/45) on the count of facets that actually reach the surface, so it is a pure function of facet count and nothing else.