Yes. Moissanite passes a standard thermal conductivity diamond tester. That surprises people, so here's exactly why it happens, what it means, and whether it should worry you as a buyer.
How standard testers actually work
The most common gemstone tester measures thermal conductivity, how quickly heat moves through a stone. Diamond has exceptionally high thermal conductivity compared to glass, cubic zirconia, and most other diamond simulants, and standard testers use that property to identify it. Moissanite's thermal conductivity, at roughly 490 W/mK, sits close enough to diamond's range of 1,000 to 2,600 W/mK, and far above cubic zirconia's roughly 8 W/mK, that it's enough to trigger a positive reading on many thermal testers.
Why this happens
Moissanite is silicon carbide. Diamond is carbon. Different materials, different atomic structures, but both happen to have high thermal conductivity by gemstone standards. That similarity is a coincidence of physics, not a design choice, and it's practically significant only because thermal conductivity is the measurement most basic testers rely on. It's worth being clear: this isn't a defect or a way of disguising the stone. Moissanite is sold explicitly as moissanite, and cubic zirconia, the actual diamond simulant most people worry about, fails standard thermal testers outright. Moissanite's overlap with diamond on this one measurement reflects a genuine physical similarity, nothing more.
What actually tells the two apart
Dual-mode testers that measure both thermal and electrical conductivity separate moissanite from diamond reliably. Diamond is an electrical insulator. Moissanite is a semiconductor with measurable electrical conductivity, and that difference is what a proper dual-mode tester picks up. These are widely available and affordable for any jeweller who wants one. Under magnification, an experienced jeweller can also identify moissanite by its double refraction, a loupe is often a more reliable tool than a basic thermal tester alone.
Does it matter for you as a buyer?
In practice, rarely. Every moissanite we set is GRA certified, and that certificate identifies the stone definitively as silicon carbide moissanite, documents its quality characteristics, and stays with the ring permanently. The diamond tester question matters more in second-hand or uncertified contexts, where a buyer has no paperwork to rely on. For a documented commission from us, it's academic: you already know exactly what you have. See our certification page for how that documentation works.
Frequently asked questions
Does moissanite pass a diamond tester?
Yes, standard thermal conductivity testers, because its thermal conductivity is high enough to register similarly to diamond.
Why does moissanite pass a diamond tester?
Its thermal conductivity is much higher than most gemstones, high enough to trigger a positive result on devices calibrated to spot diamond by heat transfer alone.
Can you tell moissanite from diamond with a tester?
Not with a standard thermal tester. A dual-mode tester measuring thermal and electrical conductivity will distinguish them reliably.
Is it deceptive that moissanite passes a diamond tester?
No. It's sold as moissanite with full GRA certification. Passing a thermal tester is a shared physical property, not something designed to mislead anyone.
How can you definitively identify a moissanite?
A GRA certificate is the definitive document. A dual-mode tester or a loupe examination by an experienced gemologist can also confirm it on an unmounted stone.
Every stone in our moissanite engagement ring collection ships with full GRA certification, so there's never any guesswork. Read more about how certification works, or start a free design consultation to begin your own ring.