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Yes, moissanite passes a standard diamond tester. On the pen-style testers most jewellers keep on the counter, a moissanite stone reads as diamond, and it does so reliably rather than by accident.
Those testers measure one thing: how quickly a stone carries heat away from a heated probe tip. Diamond is the best thermal conductor of any known material at roughly 2,000 W/m·K. Moissanite runs between 200 and 500 W/m·K depending on its crystal form — lower than diamond, but hundreds of times higher than cubic zirconia, white sapphire or glass, which is what those testers were built to catch. Moissanite clears the same threshold, so the needle goes to DIA.
A dual tester separates them in about two seconds. It adds a second probe that checks electrical conductivity, and this is where the two part company: moissanite conducts electricity and diamond does not. Most articles on this subject state it the other way round. They are wrong, and the direction matters if you are trying to identify a stone.
Why does moissanite pass a thermal diamond tester?
A thermal tester heats a small metal tip and presses it against the stone, then measures how fast heat drains out of the tip. Materials that pull heat away quickly register high; materials that insulate register low.
The gap those testers were designed to detect is enormous. Diamond sits near 2,000 W/m·K. Cubic zirconia sits near 2. Glass is around 1. Against that spread, a single threshold separates diamond from almost every simulant on the market, which is why a thirty-dollar pen works at all.
Moissanite is silicon carbide, and silicon carbide is one of very few materials that lives in diamond's neighbourhood thermally. A threshold set low enough to exclude cubic zirconia cannot exclude moissanite. The tester is not faulty. It is answering the only question it was ever built to ask.
What happened when we tested our own moissanite
Rather than describe this in the abstract, we ran it on a piece from our own stock: a moissanite eternity band in 925 sterling silver with rhodium plating, set with round-cut stones.
The instrument was a pen-style thermal-only tester of the common Diamond Selector II pattern — the type sold for under thirty dollars and used behind a great many jewellery counters. The bar climbed through the green and orange segments and stopped in the red, at the mark labelled DIA.
By that instrument's reading, our moissanite is a diamond. We photographed it because it demonstrates the point better than any explanation: passing a thermal diamond tester tells you a stone is not cubic zirconia. It does not tell you the stone is a diamond.
We sell that ring as moissanite, describe it as moissanite on the listing and the invoice, and it still lights the DIA segment. Those two facts are not in conflict. Anyone selling moissanite as diamond on the strength of a tester reading is relying on you not knowing the difference.
How does a dual tester tell moissanite from diamond?
A combination tester runs the thermal check first, then applies a small electrical potential across the stone and measures whether current flows.
Silicon carbide is a wide-bandgap semiconductor, with a band gap between roughly 2.3 and 3.3 eV depending on polytype. It conducts. Diamond is an electrical insulator and does not.
So the logic runs: thermal positive plus electrical positive means moissanite. Thermal positive plus electrical negative means diamond. It is quick and it is decisive.
| Property | Diamond | Moissanite | Cubic zirconia |
|---|---|---|---|
| Composition | Carbon | Silicon carbide | Zirconium dioxide |
| Thermal conductivity | ~2,000 W/m·K | 200–500 W/m·K | ~2 W/m·K |
| Conducts electricity | No | Yes | No |
| Mohs hardness | 10 | 9.25 | 8–8.5 |
| Thermal-only tester reads | Diamond | Diamond | Not diamond |
| Dual tester reads | Diamond | Moissanite | Not diamond |
Can a real diamond fail and read as moissanite?
Yes, and it is worth knowing before you distrust a stone on a single reading.
Type IIb diamonds contain trace boron, which makes them semiconductors. They conduct electricity, so a dual tester can flag a genuine diamond as moissanite. Some laboratory-grown diamonds carry enough boron from the growth process to do the same, at concentrations far too low to tint the stone visibly.
This is uncommon, but it is why a tester result is a strong indication rather than a certificate. If a stone genuinely matters — an heirloom, an engagement ring, anything you intend to insure — the answer comes from a gemmological laboratory, not from a pen.
Does passing a diamond tester mean moissanite is fake?
No. Moissanite is a real gemstone, not an imitation of anything.
It is silicon carbide, first identified by Henri Moissan in material from a meteorite crater, and what is grown for jewellery today is the same compound. It scores 9.25 on the Mohs scale, among the hardest materials used in jewellery, which is why it holds up to daily wear in pieces like a tennis bracelet, a heavier Miami cuban link, or an everyday marquise-cut ring. It also disperses light more strongly than diamond does, which is why moissanite throws more coloured fire.
A stone being distinct from diamond is not the same as a stone being fake. The failure here is not moissanite's. It is a one-dimensional instrument being asked a question it cannot answer, and occasionally a seller taking advantage of that.
How should you test a stone yourself?
If you already own a pen-style thermal tester, it will confirm a stone is not cubic zirconia or glass. That is genuinely useful, and it is the limit of what it can tell you.
To distinguish moissanite from diamond you need a tester that checks electrical conductivity as well, sold as a moissanite tester or a dual tester. Test on a clean, room-temperature stone — a stone warm from a hand or a pocket can skew a thermal reading — and press the probe flat against the table facet rather than an angled side.
Then, before you act on any of it, ask the seller what the stone is. A seller who will not answer plainly has told you something no tester can.
Our moissanite, sold as moissanite
Every moissanite piece we make is described as moissanite in the listing, on the invoice and in conversation. All of it is set on 925 sterling silver and ships from Canada.
Moissanite eternity bandthe ring in the photograph above, in three stone sizes
Moissanite stud earringsthe usual first moissanite piece, in several sizes and two finishes
Moissanite tennis braceleta continuous line of prong-set stones, three widths
Marquise-cut moissanite ringan elongated cut that reads larger on the finger
Floating solitaire necklacea single stone in a near-invisible setting
Moissanite cross pendantone size, in gold or rhodium tone
Sterling silver moissanite crosstwo cross sizes, on a 16–18 inch or 20 inch chain
Moissanite Miami cuban link braceletthe heaviest piece we make, in two widths
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.
Every one of them will read as diamond on a thermal tester. We would rather tell you that ourselves than have you find out from a jeweller.
Common questions
Does moissanite pass a diamond tester?
Yes on a thermal-only tester, which is the common pen type. It reads as diamond because silicon carbide conducts heat well enough to clear the same threshold the tester uses to rule out cubic zirconia. A dual tester that also checks electrical conductivity identifies it as moissanite.
Does moissanite conduct electricity?
Yes. Silicon carbide is a wide-bandgap semiconductor with a band gap of roughly 2.3 to 3.3 eV, so it conducts. Diamond is an electrical insulator and does not. Many sources state this the other way round, and they are mistaken.
Can a jeweller tell moissanite from diamond by eye?
An experienced jeweller with a loupe often can, working from moissanite’s stronger dispersion and, in many stones, doubled facet edges visible through the crown. It is not reliable enough to depend on, which is why testers exist.
Is moissanite a fake diamond?
No. Moissanite is a distinct gemstone — silicon carbide rather than carbon — with its own optical and physical properties. It is only a fake if someone sells it to you as diamond.
Will a real diamond ever fail a moissanite tester?
Occasionally. Type IIb diamonds contain trace boron, which makes them semiconductors, so a dual tester can read a genuine diamond as moissanite. A gemmological laboratory settles it.
Which moissanite piece should you start with?
If you have never owned moissanite and want to see how it behaves in daylight before committing to something larger, stud earrings are the sensible starting point. Earrings take less physical contact than rings or bracelets, and a stud puts the stone where you will notice its fire without it dominating everything you wear.
For a first piece you intend to wear every day, the floating solitaire sits under a collar and reads as understated. If you want the stone to be the point, the eternity band carries stones the whole way round and throws light from every angle.
Any of them will read as diamond on a thermal tester. That is the nature of the material, not a claim we are making about what they are.
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 thermal and electrical figures in this article are drawn from published materials-science measurements rather than jewellery marketing copy. Thermal conductivity values for silicon carbide vary with polytype and purity; the 200–500 W/m·K range reflects that spread. Band-gap figures for silicon carbide are likewise polytype-dependent, spanning roughly 2.3 to 3.3 eV. The semiconducting behaviour of boron-bearing type IIb diamond is long established in the gemmological literature.
