Does moissanite pass a diamond tester?
Yes, on a standard thermal diamond tester: moissanite conducts heat far better than other diamond look-alikes ( about 320 to 350 W/m·K, diamond about 2,200), enough to trip a thermal tester's "diamond" reading. That is why listings boast that their moissanite "passes the diamond tester"; every moissanite does. An electrical moissanite tester flags most moissanite because silicon carbide conducts electricity and diamond does not, though some moissanite reads weakly on electrical testers. A 10x loupe showing doubled facet edges is the easy home check.
How the two testers work
A thermal tester measures how fast a heated tip loses heat into the stone. Diamond is the best heat conductor of any gem. Moissanite conducts far less heat than diamond but far more than other diamond look-alikes, enough to cross the tester's threshold, so both read "diamond". A moissanite tester adds an electrical test: silicon carbide conducts a small current and diamond does not.
Where the electrical test can fail
Some moissanite reads weakly on electrical testers, so a few stones read as diamond on a basic tester. The other way round, blue diamonds contain boron and conduct electricity, so they can be misread as moissanite.
The certain checks
At home: a 10x loupe, looking through a side facet at the back edges, which double in moissanite and never in diamond. For certainty: a gem laboratory, which uses spectroscopy.
Frequently Asked Questions
Can a jeweler tell moissanite from diamond?
Yes, with a loupe (doubling) or a moissanite tester, usually in under a minute. Moissanite's extra rainbow fire under a spotlight is another clue to a trained eye.
Is "passes the diamond tester" a good sign?
It tells you nothing about quality: all moissanite passes a thermal diamond tester. Judge the listing on metal, setting, colour claim and return policy instead.
Sources
- Wikipedia: Silicon carbide (thermal conductivity by polytype, 320 to 348 W/m·K)
- Wikipedia: Material properties of diamond (thermal conductivity about 2,200 W/m·K)
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