It’s one of the most searched questions about moissanite, and the short answer is: moissanite passes most basic diamond testers, but not all of them. Whether it “passes” depends entirely on which kind of tester is used. Here is how each test works, why moissanite behaves the way it does, and why we think the honest way to wear moissanite is to call it moissanite.
Why moissanite fools a basic diamond tester
The classic handheld diamond tester (often a pen-shaped device with a metal tip) measures thermal conductivity: how quickly the stone draws heat away from the tip. Diamond conducts heat extremely well, far better than glass, cubic zirconia or most other gemstones, so the tester lights up “diamond” when heat disappears fast.
Moissanite also conducts heat very well, close to diamond. So on a thermal-only tester, moissanite usually reads as diamond. This is a property of the material, not a trick: moissanite (silicon carbide) is simply an excellent heat conductor.
Why a multi-tester catches it
Because moissanite fooled the early testers, newer devices also measure electrical conductivity. Diamond is an electrical insulator (with rare exceptions), while moissanite is a semiconductor and lets a small current through. A “multi-tester” or dedicated moissanite tester checks both, and will usually show moissanite rather than diamond.
| Test | What it measures | Moissanite result |
|---|---|---|
| Thermal diamond tester | How fast heat moves through the stone | Usually reads as diamond |
| Multi-tester / moissanite tester | Heat plus electrical conductivity | Usually reads as moissanite |
| Loupe or microscope (jeweller) | Facet “doubling” and inclusions | Doubling identifies moissanite |
| Gem lab instruments | Spectroscopy, refractive index and more | Identified as moissanite |
How a jeweller tells the difference by eye
You don’t always need a device. An experienced jeweller can often spot moissanite with a 10x loupe:
- Double refraction. Moissanite is doubly refractive, so when you look through the stone at an angle, the facet edges at the back appear doubled, like a slightly out-of-focus image. Diamond is singly refractive and shows crisp, single lines.
- Extra fire. Moissanite splits light into rainbow colours more than twice as much as diamond. In bright light, especially sunlight, that extra colour is a clue.
- Weight. For the same size, moissanite weighs roughly 10% less than diamond, which a jeweller with a scale can measure.
None of these makes moissanite look worse. They are simply what makes it a different gemstone. Our moissanite vs diamond guide explains the differences in more detail.
Does it matter if moissanite passes a diamond tester?
For most people, no. You buy moissanite because it looks bright, wears well and costs a fraction of a diamond, not to pass a test. Where it does matter is honesty:
- If you sell or trade a piece, always describe moissanite as moissanite. Selling it as diamond is misrepresentation, whatever a tester says.
- If you’re buying second-hand “diamond” jewellery, ask for a multi-tester check or an independent lab report, because a thermal tester alone can’t rule out moissanite.
We sell every stone as moissanite, and you’ll see “moissanite” in the name of every piece in our store.
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Is moissanite a real gemstone, then?
Yes. Moissanite is a real gemstone with its own chemistry and properties. It is lab-created, rated 9.25 on the Mohs hardness scale (harder than sapphire and ruby), and keeps its sparkle for life with simple cleaning. “Real” and “diamond” are not the same thing: moissanite is a real moissanite.
Frequently asked questions
It depends on their equipment. An older thermal tester will usually read moissanite as diamond; most professional buyers now use multi-testers, which identify moissanite. Either way, it should be described as moissanite.
No. Testers only touch the surface with a small probe and don’t harm the stone.
Almost all modern moissanite reads as diamond on thermal-only testers and as moissanite on electrical multi-testers, but results can vary with the device, the battery and how it’s used.
Lab-grown diamonds are chemically diamond, so they test as diamond on standard testers. Telling lab-grown from mined diamond needs specialist lab equipment.
Shop moissanite with confidence
Whether you want an everyday ring or a fully iced-out moissanite watch, you’ll know exactly what you’re buying. Explore our moissanite jewellery for men and moissanite jewellery for women, with free worldwide shipping and 15-day returns.
