Moissanite is not a fake diamond — it's a different gemstone altogether: silicon carbide, almost always laboratory-grown, with its own optics, its own strengths and its own price logic. The honest comparison most sellers won't give you is that moissanite is neither "just as good as diamond" nor "an obvious imitation" — it's a distinct material you should buy, or not buy, with clear eyes. As a gemmologist, here is exactly how the two differ, how to tell them apart, and where lab-grown diamond fits as the third option.
What moissanite actually is
Silicon carbide (SiC) was first identified in nature by the French chemist Henri Moissan in 1893, examining fragments from a meteor crater in Arizona — he initially mistook the glittering crystals for diamond, which set the tone for the next 130 years. Natural moissanite is vanishingly rare, so every stone you'll ever see in jewellery is laboratory-grown. That's not a criticism; it's simply what the product is.
Moissanite vs diamond: the side-by-side
| Property | Diamond | Moissanite |
|---|---|---|
| Composition | Carbon | Silicon carbide |
| Hardness (Mohs) | 10 | 9.25–9.5 |
| Refractive index | 2.42, singly refractive | ~2.65–2.69, doubly refractive |
| Dispersion (fire) | 0.044 | 0.104 — more than double |
| Typical price | Benchmark | Roughly a tenth or less |
| Passes basic thermal tester | Yes | Yes — this is the trap |
Two of those rows do most of the work. The dispersion figure means moissanite throws more than twice the coloured "fire" of diamond — under downlights it produces the rainbow disco-ball effect people either love or find unmistakably un-diamond-like. The double refraction means light splits in two inside the stone; look down through a moissanite with a loupe and the back facet edges appear doubled, like mild double vision. Diamond never does this. It's the single most reliable bench test there is, and one I've used thousands of times.
"Does it pass a diamond tester?" — the honest answer
A basic thermal tester reads heat conduction, and moissanite conducts heat like diamond, so yes — it will often read "diamond" on a cheap pen tester. This is how mixed parcels and misrepresented stones get through. Proper multi-testers add an electrical conductivity check that catches moissanite, and a gemmologist's loupe catches it in seconds via facet doubling. The lesson isn't that moissanite is deceitful — it's that verification belongs with someone qualified, a point I've made in my diamond clarity guide too. Any legitimate seller labels moissanite as moissanite.
Durability in real life
At 9.25+ on the Mohs scale, moissanite is harder than sapphire and entirely capable of decades of daily wear — it will not "go cloudy" (that reputation belongs to cubic zirconia, a much softer and entirely different material that does degrade with wear). Older moissanite had a faint greenish-yellow cast in some light; current premium material is genuinely colourless. On pure engineering grounds, it's a perfectly sound engagement stone.
The third option: lab-grown diamond
The comparison that actually matters in 2026 is a triangle, not a line. A lab-grown diamond is real diamond — carbon, hardness 10, singly refractive, identical fire and brilliance — grown in weeks rather than aeons, and priced well below natural. It has compressed moissanite's advantage: where moissanite once competed against natural diamond prices, it now competes against lab-grown ones, and the gap is far narrower than it was. My plain-language take on how natural, lab-grown and imitation stones relate is in my gemmologist's glossary.
How I frame the choice for clients: if you want diamond — its specific, quieter white brilliance, its permanence of meaning — choose natural or lab-grown according to budget and values. If you love the livelier rainbow fire and the price point, and you're happy owning a stone that is proudly its own species, moissanite is a legitimate choice. What I won't do is sell one dressed as the other.
Where Lucano stands
I work in natural and lab-grown diamonds, and in traceable coloured stones — that's where my supply chain and my certifications live, and verifiable sourcing is the whole point of this business. If you're weighing moissanite against a diamond for an engagement ring, I'm genuinely happy to walk you through both under the loupe at a bespoke consultation — you'll see the facet doubling and the fire difference yourself in about thirty seconds, and you'll make the decision informed rather than sold.
Moissanite vs diamond FAQ
Can people tell moissanite from diamond?
At a glance across a dinner table, usually not. Under downlights or sunlight, the stronger rainbow fire is noticeable to anyone who knows what they're looking at — and unmistakable to a jeweller with a loupe.
Does moissanite get cloudy over time?
No. That's cubic zirconia's failure mode. Moissanite's surface hardness and chemistry keep it bright indefinitely with normal cleaning.
Is moissanite worth anything for resale?
Very little — it's a manufactured product with ongoing supply. Diamonds hold value imperfectly but meaningfully; moissanite should be bought for enjoyment, not as a store of value.
Moissanite or lab-grown diamond — which should I pick?
If the budget stretches to lab-grown and what you want is a diamond, pick the diamond. If the rainbow fire delights you or the budget is firm, moissanite is a fine stone honestly worn as itself.
