Does Moissanite Pass a Diamond Tester?
On a basic thermal diamond tester, yes: moissanite conducts heat almost exactly like diamond, so the tester reads "diamond". On a dual or multi-tester, which also measures electrical conductivity, no: moissanite conducts electricity and nearly all diamonds do not, so the tester identifies it as moissanite.
How a diamond tester works
The classic handheld tester is a thermal probe. Its tip is heated, touched to the stone, and the instrument measures how quickly the stone draws the heat away. Diamond is one of the best thermal conductors known, far better than glass, cubic zirconia, sapphire or almost any other gem, so for decades a thermal probe was a quick, reliable way to separate diamond from its imitations.
Why moissanite reads as diamond
Moissanite's thermal conductivity is close enough to diamond's that thermal probes respond to it as if it were diamond. GIA noted this in 1997, when gem moissanite first appeared: the testers then on the market gave a "diamond" reaction. Nothing about the stone is designed to deceive; the two materials simply share this property.
The test that tells them apart
Moissanite is a semiconductor; diamond is an electrical insulator. A dual tester (often sold as a diamond/moissanite tester) runs the thermal test, then passes a tiny current through the stone. If the stone conducts, the tester flags moissanite.
| Tester | Diamond | Moissanite | Cubic zirconia |
|---|---|---|---|
| Thermal only | Diamond | Diamond | Not diamond |
| Dual: thermal + electrical | Diamond | Moissanite | Not diamond |
There are two edge cases worth knowing:
- Type IIb diamonds contain boron, which makes them conduct electricity. They include rare natural blue diamonds and some laboratory-grown diamonds, and an electrical tester can wrongly flag them as moissanite.
- Contact with metal. If the probe touches a prong or the band while testing a set stone, the metal can complete the circuit and produce a false "moissanite" reading.
That is why professionals treat a tester as a first check, not a verdict.
Other ways a jeweller can tell
- A loupe. Moissanite is doubly refractive: viewed through the side of the stone, the back facet edges can look doubled. Diamond is singly refractive and shows crisp single edges.
- Weight against size. A loose moissanite weighs about 9% less than a diamond of identical dimensions.
- Fire. Moissanite's dispersion is more than twice diamond's; in strong light the difference in coloured flashes is visible to a trained eye.
- A laboratory report. The definitive answer comes from a gem lab using spectroscopy.
What this means for you
If you own moissanite, a thermal tester reading "diamond" says only that the stone conducts heat very well. If you want certainty about any stone, ask for a dual test and look at its documentation. Every Luhusati piece is sold as moissanite and arrives with a GRA report stating its colour and clarity.