This is the question we get asked most on our live shows, and it deserves a straight answer rather than a sales pitch.
The short answer
On a cheap thermal diamond tester — the pen-shaped kind you see on market stalls and in most eBay listings — yes, moissanite will usually read as diamond. On a modern dual tester that also measures electrical conductivity, no. It reads as moissanite immediately.
Why the cheap testers get it wrong
Basic diamond testers do one thing: they measure how fast heat moves through a stone. Diamond conducts heat exceptionally well. So does moissanite — the two are close enough that a thermal-only probe cannot separate them.
That is not a flaw in moissanite. It is a genuine physical property of silicon carbide, and it is the same reason moissanite feels cool to the touch the way a diamond does.
Why the better testers get it right
Diamond does not conduct electricity. Moissanite does. A dual-probe tester checks both thermal and electrical conductivity, and the moment it applies the electrical test the two stones separate cleanly. Any competent jeweller has one.
Where this gets misused
Some sellers use the first fact to imply their stone is a diamond. They wave a cheap tester at it on camera, it beeps, and the implication hangs in the air.
We think that is dishonest, and it is also bad business. If you buy a piece believing it is a diamond and later discover it is not, you will never buy from that seller again — and you will tell people.
Everything we sell is moissanite. We say so in the product title, the description and on camera. We are happy to run a tester on air and explain exactly what the beep does and does not prove.
Does it matter for insurance or valuation?
Yes, and this is worth knowing. Moissanite has a fraction of the resale value of a mined diamond, so do not insure a moissanite piece as though it were one. If you need a formal valuation, a gemmological lab will identify the stone correctly in minutes.
The practical takeaway
If someone is selling you a diamond and their only proof is a thermal tester, ask for a dual tester or a certificate. If they will not provide one, walk away.
And if you are buying moissanite knowingly — because you want the sparkle, the hardness and the price — the tester question is irrelevant. You already know exactly what you are getting.