It is one of the most common questions people ask before buying: will a moissanite set off a diamond tester? Understanding the answer means understanding how those testers actually work — and once you do, moissanite’s reputation as a serious stone makes a lot more sense.

How basic diamond testers work

The classic, inexpensive pen-style tester does not actually detect diamonds. It measures thermal conductivity — how quickly a stone moves heat. Diamond conducts heat extremely well, so the tester is calibrated to flag stones that behave that way. The catch is that moissanite also conducts heat very efficiently, which is why these older testers frequently read moissanite as diamond.

Why newer testers tell them apart

Because that overlap became well known, modern testers added a second measurement: electrical conductivity. Moissanite conducts electricity in a way diamond does not, so a dual tester checks both properties and can distinguish the two reliably. A jeweler with current equipment will identify moissanite correctly — it is not designed to fool anyone, and a reputable seller never markets it as a diamond.

What this tells you about quality

The fact that moissanite shares diamond’s heat behavior is not a trick — it reflects genuinely diamond-like physical properties. Moissanite is one of the hardest materials used in jewelry, holds a brilliant polish, and throws even more colorful fire than diamond. Passing an old-style tester is simply a side effect of being a high-performing stone, not a flaw to hide.

Can you tell by eye?

Side by side, a trained eye may notice moissanite’s extra flashes of rainbow color, especially in larger stones and bright light. In everyday wear, on a hand in motion, almost no one is examining the difference. What people actually see is a bright, lively, beautiful stone — which is the whole idea.

Frequently asked questions