Moissanite has a higher refractive index than diamond — 2.65 against 2.42 — so almost any moissanite sparkles. That is the easy part. The hard part is that the cut also decides how white the stone looks and how much of its fire you can actually see.
How cut controls light
A stone's job is to take light in through the crown, bounce it off the pavilion facets, and throw it back at you. Three numbers govern whether that works.
- Table — the flat top facet. Too large and light leaks out the sides.
- Crown angle — the slope from girdle to table. For a round brilliant, 33.5 to 35 degrees is the working range.
- Pavilion depth — where the light actually turns around. Get this wrong and the middle of the stone goes dark.
None of these are visible to the naked eye, which is why a badly cut moissanite can still be listed as "excellent cut" without anyone being able to argue.
Round brilliant: the reference point
Fifty-seven or fifty-eight facets, and a century of optical work behind the angles. A well-made round brilliant hides colour better than any other shape because the pavilion mains reflect light straight back through the centre, and the eye reads that bright return as whiteness.
The trade-off is price and ubiquity. A round costs more per millimetre than a fancy shape of the same spread, because more of the rough is ground away. It is also the least distinctive choice on the finger, which some buyers mind and most do not.
Oval: spread without the weight
An oval wears larger than its millimetres suggest. A 7.7mm by 5.7mm oval has a long axis most rounds cannot match, and that length flatters short fingers. Look for a ratio between 1.35 and 1.50; below that you have an egg, above it you have a canoe.
Ovals expose more of the stone's body than rounds. The ends of an oval are shallow, and shallow areas show a warm cast more readily. On a near-colourless stone this is where you will notice the tint first. Also check for a dark band across the middle, known as a bow-tie, which happens when the pavilion is cut too steeply across the short axis.
Radiant: the best of the angular cuts
Radiant is a brilliant-style cut with trimmed corners. It keeps brilliant facet patterns, so it retains the light return of a round, but it is rectangular and looks bigger face-up for a given weight. The cut corners also solve the chipping problem that plagues square-cornered stones.
Radiant is the most forgiving fancy shape for moissanite. It spreads well, hides colour reasonably, and photographs with visible facet structure rather than a flat sheet of sparkle. If you want something that is not a round and you do not want to think hard about the trade-offs, this is the shape.
Emerald: beautiful, and unforgiving
Step-cut facets, straight lines, a hall of mirrors. An emerald cut in moissanite is a striking thing when the material is clean and the cut is accurate.
It is also the shape that shows colour most openly. Step facets act like windows: they carry your eye down into the stone rather than bouncing light back off. That means body colour is visible in a way it never is in a round. Buy emerald-cut moissanite in the top colour grade or not at all, and expect the cut to look smaller per millimetre than a radiant of the same width.
The other emerald risk is bow-tie-style extinction. Long step facets on a shallow pavilion go dark in bands. Worth viewing the stone rotating in daylight before committing.
Matching the cut to the hand and the setting
| Cut | Light return | Hides colour | Reads big per mm |
|---|---|---|---|
| Round brilliant | Highest | Best | Average |
| Oval | High | Moderate | High |
| Radiant | High | Good | High |
| Emerald | Moderate | Poor | Moderate |
Two practical notes from the bench. A halo setting adds a ring of small stones around the centre and makes any cut read a size larger, which is often a better use of budget than buying a bigger centre stone. And a bezel setting around an emerald or radiant protects the corners far better than four thin prongs on a stone worn daily.
What to ask a seller
- Which cut grade, and judged by whom? "Excellent" without a grader named means nothing.
- What are the table percentage and depth percentage?
- Can I see the stone rotating in daylight, not under a display lamp?
- Is there a bow-tie, and how pronounced?
One honest point to close on. A brilliantly cut moissanite in a mid colour grade will outperform a mediocre cut in the top grade, every time. Cut first, colour second. That ordering is the single most useful thing to take away from this page.