You're standing in a jewelry store, or maybe you're staring at a screen, trying to figure out if that sparkling rock is actually worth the three months' salary people used to talk about. It’s stressful. Honestly, the gap between "natural treasure" and "lab-created marvel" has narrowed so much that even some seasoned pros get a little sweat on their brow when a high-quality moissanite hits their desk.
If you want to know how to tell a moissanite from a diamond, you first have to accept that they aren't the same thing. Moissanite isn't a "fake" diamond. It’s a different mineral entirely—silicon carbide—originally found in a meteor crater by Henri Moissan in 1893. Since space rocks are hard to come by, the stuff we buy today is grown in labs like those run by Charles & Colvard.
Diamonds are pure carbon. They’re harder, they’re older, and they play with light differently. But to the naked eye? They’re basically twins. If you’re trying to spot the difference at a brunch table or under the harsh LEDs of a jewelry counter, you need to know exactly what to look for, because the "spud test" or the "water test" you saw on TikTok is probably nonsense.
The Rainbow Connection and the Double Refraction Trick
Diamonds are famous for their "fire," which is just a fancy way of saying how they break light into colors. But moissanites are actually more refractive. They’re like diamonds on espresso.
When light hits a moissanite, it splits into two rays. This is called birefringence or double refraction. If you look through the side of a moissanite with a jeweler’s loupe (or even a high-quality macro lens on your phone), you might see the back facets looking "doubled." It’s a subtle blurriness that diamonds—which are singly refractive—simply do not have.
Then there’s the "disco ball effect."
If you take both stones into the sunlight, the moissanite is going to throw off intense, rainbow-colored flashes. It’s a literal light show. Diamonds produce a more balanced mix of white light (brilliance) and colored light (fire). If the stone looks like it’s trying to start a rave on your ceiling, it’s probably a moissanite.
Weight Matters More Than You Think
Here is a weird fact: moissanite is about 15% lighter than diamond.
If you have two stones of the exact same dimensions—let’s say 6.5mm rounds—the diamond will weigh 1.00 carat. The moissanite, however, will only weigh about 0.88 carats.
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This is why reputable moissanite sellers often sell by "Millimeters" or "Diamond Equivalent Weight" (DEW) rather than actual weight. If you put a "1-carat" moissanite on a sensitive digital scale and it weighs significantly less than a 200mg (the weight of a 1-carat diamond), you’ve found your answer.
It’s physics. You can’t fake density.
Looking for the Flaws
We’ve been conditioned to think that "perfect" means real. In the world of gemstones, it’s usually the opposite.
Natural diamonds almost always have "birthmarks" called inclusions. We're talking about tiny bits of carbon, feathers, or clouds that got trapped in the stone billions of years ago. Lab diamonds have them too, though they look a bit different.
Moissanites are grown in highly controlled environments. Their "flaws" are different. Instead of carbon spots, you might see tiny, needle-like structures that are white or translucent. These are "pipe-like" inclusions that occur during the growth process.
What to check for with a 10x Loupe:
- Facet Junctions: Diamonds are the hardest material on Earth. Their facet edges (where the flat faces meet) are incredibly sharp and crisp. Moissanite is very hard (9.25 on the Mohs scale), but it's not a diamond. Over time, or even right out of the gate, the facet junctions on a moissanite might look slightly more rounded or "soft" compared to the razor-sharp lines of a diamond.
- The Girdle: Look at the "waist" of the stone. Many diamonds have a frosted or polished girdle with a laser inscription (like a GIA report number). Moissanites often have a different texture here, sometimes appearing a bit more "waxy" under high magnification.
The Thermal and Electrical Conductivity Test
Most people think a "diamond tester" is a magic wand. It’s not.
Old-school testers measured thermal conductivity. Since moissanite conducts heat very similarly to diamond, it would often "pass" as a diamond on those cheap $20 pens you buy on Amazon.
Modern jewelers use multitesters. These measure both heat and electricity. Moissanite is a semiconductor, meaning it conducts electricity in a way that diamonds (mostly) don’t. A professional-grade tester like the Presidium Gem Tester II can usually tell the difference in seconds.
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However, be careful. Some of the newest "super-moissanites" or specific types of lab-grown diamonds (Type IIb) can sometimes trick these sensors. Never rely on a beep alone.
Color and the "Oil Slick" Phenomenon
Back in the day, moissanites had a tell-tale yellow or green tint. If you saw a stone that looked a bit like it had been soaked in weak tea, it was a moissanite.
That’s over. Modern "Forever One" or "Amora" stones are icy white.
But moissanite has a weird quirk: it’s lipophilic. That’s a fancy way of saying it loves oil. It attracts skin oils, lotions, and dirt like a magnet. When it gets dirty, it can develop a hazy, bluish-grey film on the surface that looks a bit like an oil slick on a puddle.
Diamonds get dirty too, but they don't usually get that specific "film" look. A quick scrub with a toothbrush and some mild dish soap usually fixes it, but the frequency of the "film" is a classic moissanite trait.
Why the Price Tells the Story
Let’s be real. If you’re looking at a 2-carat, D-color, VVS1-clarity stone and the price is $400, it is not a diamond. It’s not even a "discounted" diamond. It’s a moissanite or a CZ.
A natural diamond of that quality would easily fetch $20,000 to $40,000 depending on the cut. A lab-grown diamond would still be in the $800 to $1,500 range.
Moissanite is a budget-friendly powerhouse, but it’s priced as a manufactured product, not a mined rarity. If the price feels too good to be true, your eyes aren't deceiving you; the math is just doing its job.
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Understanding the "Hardness" Gap
Diamonds are a 10 on the Mohs scale. Moissanites are a 9.25.
That sounds close, right? In reality, the scale is not linear. A diamond is actually several times harder than a moissanite.
If you look at an older piece of jewelry that has been worn for five or ten years, look at the "crown" (the top) of the stone. A diamond will almost always be pristine, with no scratches. A moissanite might show tiny "nicks" or abrasions on the facet edges where it has knocked against car doors or granite countertops.
It’s durable enough for daily wear, sure. But it’s not "forever" in the same way carbon-to-carbon bonds are.
How to Actually Check Your Stone Right Now
If you have a stone in front of you and you're suspicious, don't panic. Take a breath.
First, get a piece of white paper. Put the stone face down (pointy side up) and look through the bottom. If you see a dark "donut" or a lot of grey, it might be a poorly cut diamond or a moissanite.
Second, find a pen light or even just your phone's flashlight. Hold the stone about a foot away from a white wall in a dark room. Shine the light through the top of the stone.
Look at the reflections on the wall.
- Diamond: You'll see white sparks and some distinct, sharp rainbow shapes.
- Moissanite: You'll see a lot more "fire." The rainbows will be more numerous, longer, and look like they’re doubled.
Actionable Steps for the Skeptical Buyer
If you are buying a stone and want to ensure you aren't paying diamond prices for moissanite, do these three things:
- Demand a Lab Report: If it's a diamond, it should come with a GIA, IGI, or HRD certificate. If the seller hands you a "Certificate of Authenticity" from a brand you’ve never heard of, be wary. Moissanite often comes with a GRA report, which looks official but isn't a grading entity for diamonds.
- Use a Loupe: Buy a 10x triplet loupe. They cost $15. Look for that double refraction (the blurring of the back facets). If you see it, it's moissanite. Period.
- The Fog Test: Breathe on the stone. Diamonds dissipate heat almost instantly, so the fog should clear up in a second or less. Moissanite holds onto that fog for just a beat longer. It's subtle, but if you have a known diamond to compare it to, the difference is obvious.
At the end of the day, moissanite is a gorgeous stone. It’s ethical, it’s bright, and it’s tough. But if you’re paying for a diamond, you deserve a diamond. Trust your eyes, use a loupe, and never buy a "deal" that seems impossible.