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The simplest difference: a lab-grown diamond is a real diamond, while moissanite is a different gemstone that looks similar. Both are beautiful, both are durable enough for daily wear, and both cost far less than a mined diamond — but they are not the same stone, and the gap between them widens as the stone gets larger. Here is how they compare, honestly, including the measurable properties and the one test that settles it definitively.
Key takeaways
- A lab-grown diamond is a real diamond (pure carbon); moissanite is silicon carbide — a different gem, not a lesser one.
- Diamond is the hardest material (Mohs 10); moissanite is very hard too (9.25). Both suit everyday wear.
- Moissanite has more than twice the dispersion of diamond — stronger rainbow flashes, which some love and some find too much.
- Moissanite is doubly refractive; diamond is singly refractive. This is the definitive tell under magnification.
- Top-grade modern moissanite is genuinely colourless — the old yellow-green tint complaint is largely out of date.
- The differences are most visible in large stones, which matters at three carats and above.
- Choose moissanite for a beautiful stone at the lowest price; choose a lab-grown diamond when you want a real, certified diamond.
What is moissanite?
Moissanite is a gemstone made of silicon carbide. Naturally occurring moissanite is vanishingly rare, so effectively all jewellery moissanite is grown in a laboratory. It is brilliant, hard, and a legitimately beautiful choice — it is simply a different mineral from diamond. The word simulant gets used for it, which is accurate in the technical sense that it stands in for a diamond visually, but it undersells the stone. Unlike cubic zirconia, moissanite is a serious gem in its own right that happens to resemble a diamond.
Where moissanite came from
In 1893 the French chemist Henri Moissan was examining rock from the Canyon Diablo meteorite crater in Arizona when he found tiny, brilliant crystals in the samples. He took them for diamonds. It was not until 1904 that he correctly identified them as silicon carbide — material delivered to Earth by the meteorite rather than formed here — and the mineralogist George Kunz named the mineral moissanite in his honour that same year.
Natural moissanite proved far too rare for jewellery. The stone only became a commercial gem a century later, when Charles & Colvard brought a patented growth process to market in 1998 and produced the first gem-quality moissanite. So the two stones being compared here have a shared quirk of history: both were once found only in nature in quantities too small to matter, and both became available because someone learned to grow them.
What is a lab-grown diamond?
A lab-grown diamond is chemically, physically and optically identical to a mined diamond — pure crystallised carbon, grown in a chamber rather than the earth. It is a real diamond in every sense, graded on the same 4Cs by the same laboratories. IGI grades lab-grown diamonds on the full 4C scales; GIA has used a two-tier Premium or Standard classification for them since 1 October 2025. For how they are made see CVD vs HPHT, and how they compare to mined in lab-grown vs mined.
Side by side: the measurable differences
These are standard gemological constants, not opinions — and they explain everything the eye notices.
| Property | Lab-grown diamond | Moissanite |
|---|---|---|
| What it is | Real diamond — carbon | Silicon carbide — a different gem |
| Hardness (Mohs) | 10 — the hardest material known | 9.25 — second only to diamond |
| Refractive index | 2.42 | 2.65–2.69 — higher |
| Dispersion ('fire') | 0.044 | 0.104 — more than double |
| Specific gravity | 3.52 | 3.21 — slightly lighter |
| Optical character | Singly refractive | Doubly refractive — facets appear doubled at 10x |
| Colour | Graded D–Z; can be truly colourless | Top grades colourless; lesser grades warm in large sizes |
| Certification | IGI on the full 4Cs (GIA uses a two-tier classification) | Manufacturer's certificate, not diamond-graded |
| Resale | Retains standing as a real diamond | Very limited secondary market |
Every claim here is one you can check on the certificate — and we will walk you through a real one, no obligation.
Ask us anythingDouble refraction: the definitive tell
The most useful difference is one almost nobody mentions. Diamond is singly refractive: light entering it travels as a single ray. Moissanite is doubly refractive, splitting light into two rays that travel at slightly different speeds. The practical consequence is visible under a 10x loupe: look down through the table of a moissanite at an angle and the opposite facet edges appear doubled, like a faint double-exposure. A diamond never shows this.
This matters because the older tests are unreliable. A thermal probe — the classic 'diamond tester' — reads moissanite as a diamond, because silicon carbide conducts heat almost as well as diamond does. That single fact caused years of misidentification in the trade before combined testers became standard. Facet doubling, by contrast, is a property of the material that cannot be disguised, and any trained gemmologist can confirm it in seconds.
How they look
Side by side, moissanite throws noticeably more coloured fire, and the table above says exactly why: its dispersion is 0.104 against diamond's 0.044, so it splits white light into spectral colours more than twice as strongly. In bright sun or under spotlights this reads as vivid rainbow flashes. Some people adore it. Others find it reads as something other than a diamond, because a diamond's signature is a balance of white brilliance and colour rather than a dominance of colour.
On colour, moissanite deserves a correction that is often missing from comparisons written by diamond sellers. Early moissanite had a noticeable yellow-green cast, and that reputation has stuck. Modern top-grade moissanite is genuinely colourless and holds up well against a fine diamond. The tint issue is real but now belongs to the lower grades — and, as below, to size.
Why size changes the answer
Every optical difference in the table scales with the stone. A larger gem has a longer path length for light, so whatever a material does to light, it does more visibly. In a small accent stone the two are hard to tell apart. At three carats and above, three things become easier to see: the extra fire is more pronounced, facet doubling is easier to catch, and any residual body colour in a lesser grade of moissanite has more material to show itself through.
This is worth flagging plainly because it is the case where the two stones diverge most, and it happens to be exactly the size range we work in. It is not an argument that moissanite is a poor stone. It is an argument that the comparison you read about a one-carat stone does not transfer cleanly to a three-carat one.
Durability
Both wear well for everyday rings, and this is where moissanite is genuinely strong. Diamond is the hardest known material at Mohs 10; moissanite at 9.25 is second only to diamond and comfortably above everything it will meet in daily life, including the quartz dust that gradually ruins softer stones. Neither will cloud, neither will scratch in normal wear, and both will look the same in decades as they do today. For a lifetime ring, either material is durable enough — this is not the axis on which the decision should turn.
Value and resale
Moissanite is the cheaper stone, meaningfully so, and for many buyers that is the entire point. What it does not have is a secondary market: there is little established resale for moissanite, because supply is effectively unlimited and there is no independent grading framework to price a given stone against. A diamond — lab-grown or mined — is at least a recognised, gradeable asset with a documented specification, though nobody should buy an engagement ring as an investment. We set out the honest position on that in lab-grown diamond resale value.
Which should you choose?
If your priority is the lowest price for a large, sparkly, durable white stone, moissanite is excellent value and there is no shame in choosing it. If what you want is a real diamond — the actual material, with a diamond's optical signature and an independent diamond certificate — at a fraction of mined prices, a lab-grown diamond is the answer. The honest framing is that these are two good options for different priorities, not a right answer and a compromise.
Montare works only in real, certified lab-grown diamonds, held to one fixed standard: D–E colour, VVS1–VVS2 clarity, Triple Excellent cut with table and depth in the ideal range for that shape, three carats minimum, IGI certified. The per-shape figures are published on our standards. You describe what you are looking for and we source the stone that clears it; our goldsmiths then cast, set and polish the ring by hand in Toronto. If you are also considering cubic zirconia, that is a genuinely different conversation — we cover it in lab-grown diamonds vs cubic zirconia.
Bring us any diamond you are considering — ours or someone else's — and we will read the certificate with you and show you exactly what the grades mean. No obligation.
Book a free consultation →Frequently asked questions
Is moissanite a diamond?
No. Moissanite is silicon carbide, a separate gemstone that resembles a diamond. A lab-grown diamond, by contrast, is a real diamond — chemically and optically identical to a mined one.
Can you tell moissanite from a diamond?
Often, yes — moissanite shows more rainbow fire, especially in larger sizes and bright light. The conclusive test is magnification: moissanite is doubly refractive, so its facet edges appear doubled under a 10x loupe, which never happens in a diamond.
Which is more durable, diamond or moissanite?
Both are very durable. Diamond is the hardest material at Mohs 10; moissanite is 9.25, second only to diamond. Either suits everyday wear, and neither will cloud or scratch in normal use.
Which is cheaper, moissanite or lab-grown diamond?
Moissanite is the less expensive. A lab-grown diamond costs more but is a genuine, certified diamond — and still far below mined prices.
Does moissanite look fake?
No — modern top-grade moissanite is colourless and brilliant, and the old yellow-green tint complaint applies mainly to lower grades and older material. What it does have is more than double the dispersion of diamond, so it throws stronger rainbow flashes. Whether that reads as beautiful or as visibly not-a-diamond is genuinely a matter of taste.
Do diamond testers detect moissanite?
A basic thermal-probe tester does not reliably distinguish them, because silicon carbide conducts heat almost as well as diamond and can read as a diamond. Modern combined testers add an electrical-conductivity check, and magnification shows moissanite's doubled facet edges directly.
Is moissanite a good choice for a three-carat ring?
It is durable enough at any size, but the optical differences are most visible in large stones: at three carats and above the extra fire is more pronounced and facet doubling is easier to spot. If the goal is a large stone that reads unmistakably as a diamond, that is the size range where the distinction starts to matter.
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