How to tell moissanite from a diamond by eye

Updated 13 August 2026·Written by the Aqua Gold workshop, Ontario.

Yes, with practice. Hold the stone to a jeweller's loupe at an angle and look through the crown for facet edges that appear doubled, and watch for a stronger scatter of coloured fire than a diamond of the same cut usually throws. Both signs are real physical differences. Neither is something most people catch reliably with the naked eye alone.

Both signs come from real, measurable optical differences between the two materials, not from folklore. But both take the right conditions to see, and doubling in particular takes a magnifier most people do not carry. This is the honest version of a test that gets oversimplified a lot online.

Why does moissanite throw more fire than diamond?

Fire is the rainbow flash you see when white light splits into its spectral colours as it passes through a cut stone. It is governed by a property called dispersion, and moissanite's is 0.104 against diamond's 0.044 — roughly two and a half times higher. Moissanite also has a much higher refractive index, about 2.65 to 2.69 against diamond's 2.417, which is part of why it bends and returns light so aggressively.

In a well-cut stone under mixed or point-source lighting, that difference is visible: a moissanite of any size tends to throw larger, more frequent flashes of colour than a diamond of comparable size and cut. Under flat, diffuse light — an overcast sky, a shaded room — the gap narrows and can be hard to judge with confidence.

What is "doubling" and why does moissanite show it?

Diamond crystallises in the cubic system. Optically, that makes it isotropic: light travels through it by a single path in every direction, so a diamond is singly refractive and its facet edges stay crisp and single, always.

Moissanite is silicon carbide, which crystallises in the hexagonal system. That makes it uniaxial and doubly refractive: a ray of light entering the stone splits into two rays that travel at slightly different speeds and bend by different amounts. Look through the stone at the right angle and the facet edges on the far side appear as two overlapping lines rather than one — a soft doubling, sometimes described as fuzziness, at the edges of the back facets.

This is not a subtle theoretical difference. Moissanite is doubly refractive and diamond is singly refractive, so a stone's facet edges can appear doubled under a loupe. It is the single most decisive visual test available without instruments, when you can actually see it clearly.

How do you actually see the doubling?

You need a 10x jeweller's loupe, good light, and an angle. Looking straight down through the table rarely shows it, because stones are typically cut with the table close to perpendicular to the optic axis, and doubling can all but disappear along that axis. Tilt the stone, or your line of sight, so you are looking through a crown facet toward the culet or the pavilion facets on the far side, and rotate slowly.

The doubling is easiest to see looking at an angle through the crown toward the pavilion, not straight down the table. On a small stone this takes a genuinely steady hand and a bright, close light source. On a larger stone, 6 mm and up, it is considerably easier, which is one reason people practising this test often start with a larger single-stone piece such as a 6 mm or 6.5 mm stud rather than a small accent stone.

First attempts miss it more often than not. Comparing a known moissanite side by side with a known diamond, under the same loupe and the same light, is the fastest way to learn what you are actually looking for.

Can fire alone tell you, without a loupe?

Not reliably. Fire depends on cut quality, stone size and lighting as much as on the material. A well-cut diamond in bright, mixed lighting throws real fire of its own, and a shallow or poorly proportioned moissanite can look duller than its dispersion figure suggests.

Fire alone is not a reliable naked-eye test, because cut quality and lighting change how much of it you see. Treat unusually intense rainbow flash as a reason to look closer, with a loupe, rather than as a verdict on its own.

Does an experienced jeweller always get it right by eye?

Often, but not instantly, and not with total certainty. A jeweller who inspects stones daily can usually make a confident call from dispersion and doubling together within seconds under a loupe. That confidence comes from repetition, not from either sign being infallible alone.

It also gets harder with small, densely set stones: a stone-set eternity band or a tennis bracelet holds dozens of stones in a continuous line, and inspecting each individually is slow and impractical outside a lab. For a faster, decisive answer, we've written separately about whether moissanite passes a diamond tester — a dual electrical-and-thermal tester settles it in about two seconds, which no loupe can match.

Does more fire mean moissanite is trying to look like a diamond?

No. The extra dispersion is simply a property of silicon carbide, not a design choice aimed at imitation. Moissanite is a distinct gemstone with its own optical profile, sold and described as moissanite here, not as diamond. For a fuller picture of how the two compare on hardness, price tier and resale — not just optics — see our moissanite versus lab and mined diamond breakdown.

A stone throwing more colour than another is a description, not a complaint. Some buyers want exactly that; some find it too much next to a diamond's quieter white light. Neither preference is wrong, and knowing the reason behind the difference is what lets you choose deliberately instead of guessing.

Where to practise this yourself

A single, unobstructed stone in an open setting is the easiest place to learn the test. Stud earrings hold one round stone per ear in a four-prong setting that leaves the sides open to light, which makes both the fire and, with a loupe, the doubling easier to find than in a busier piece. A floating solitaire or a marquise-cut ring offers the same single-stone clarity in a different shape.

Pieces with many smaller stones, like a full eternity band or a tennis bracelet, are worth owning and wearing, but they are a harder place to start if you are teaching yourself the loupe test. Learn it on one stone first.

• Moissanite stud earringsthe easiest single stone to practise the loupe test on
• Moissanite eternity bandstones the whole way round, in three sizes
• Moissanite tennis braceleta continuous line of prong-set stones
• Marquise-cut moissanite ringa single elongated stone in an open setting
• Floating solitaire necklaceone stone, near-invisible setting
• Moissanite cross pendantsmaller stones across the arms, gold or rhodium tone
• Moissanite Miami cuban link braceletstones set along flat interlocking links
• Sterling silver moissanite crosstwo sizes, stone-set across the face

You can browse the full range by category — rings, earrings, bracelets and necklaces — or start with our best sellers, which is where most people begin.

Common questions

More questions

We answer shipping, returns, sizing and payment questions on our FAQ page. If something is not covered there, get in touch and a person from the workshop will answer.

References

The optical figures in this article — refractive index, dispersion and birefringence for both diamond and moissanite — are drawn from published gemmological and materials-science measurements rather than jewellery marketing copy. Birefringence for silicon carbide varies with polytype and is commonly cited between roughly 0.036 and 0.043; we have used the higher, more widely cited figure while noting the range exists. Dispersion, refractive index and crystal-system figures are consistent across independent gemmological references.