Does Moissanite Pass a Diamond Tester?

Yes, on the most common kind. A basic diamond tester measures how fast a stone draws heat away, and moissanite draws heat away fast enough to read as diamond. A multi-tester, which also checks whether the stone conducts electricity, tells moissanite and diamond apart, though it has blind spots of its own. Here is how each tester works and how a jeweler confirms what a stone really is.

How a diamond tester works

The handheld testers most jewelers keep on the counter are thermal testers. A heated metal tip touches the stone and the tester measures how quickly the heat drains away. Diamond conducts heat better than any other gemstone, so it pulls heat from the tip fastest.

Thermal testers came into use in the early 1980s to separate diamond from cubic zirconia, the most common imitation at the time. Cubic zirconia conducts heat poorly, so it fails the test right away.

Why moissanite passes

Shown: Jemma Round Moissanite Solitaire Engagement Ring

Moissanite conducts heat less well than diamond, but far better than any other gemstone. That is enough to cross the line a thermal tester uses, so the tester reads moissanite as diamond. When moissanite jewelry reached the market in the late 1990s, it passed the thermal testers jewelers relied on, and the trade needed a new test.

How a multi-tester tells them apart

The answer was electricity. Moissanite conducts electricity, and most diamonds do not. A multi-tester combines a thermal probe with an electrical one: if the stone conducts heat like a diamond and also conducts electricity, the tester reads moissanite.

When a tester gets it wrong

Some real diamonds conduct electricity. Natural blue diamonds, the Hope Diamond among them, contain traces of boron, and so do many lab-grown diamonds grown under high pressure and high temperature. Boron lets a diamond conduct electricity, so these diamonds can read as moissanite on a multi-tester.

Technique matters too. If the probe touches the metal setting instead of the stone, the electrical reading can come out wrong. A handheld tester gives a quick first answer, and a jeweler confirms it another way.

How a jeweler confirms what a stone is

• A loupe. Moissanite is doubly refractive, so at 10x magnification its back facet edges look doubled from some angles. Moissanite is usually cut so the doubling is hard to see straight through the top, so the jeweler tilts the stone and looks through a side facet. Diamond, mined or lab-grown, never shows doubling.
• The paperwork. Larger diamonds usually come with a grading report from the GIA or the IGI, and lab-grown diamonds are often laser-inscribed on the girdle. A loupe reads the inscription.
• A gem lab. For a final answer, a gemological lab identifies the stone with spectroscopy.

What this means for your ring

Shown: Esme Pear Moissanite Halo Engagement Ring

If someone tests your moissanite with a basic pen tester and it reads diamond, that is the thermal reading at work. Your stone is still moissanite, a gemstone in its own right, and every Carissie product page names it that way. When you take your ring to a jeweler for cleaning or repair, tell them the stone is moissanite and the band is gold-plated sterling silver, so they choose the right cleaning method.

Common questions

Will moissanite pass a diamond tester pen?

Yes. Most pen testers measure heat conduction only, and moissanite reads as diamond on them. A multi-tester that also checks electrical conductivity identifies it as moissanite.

Can a jeweler tell moissanite from diamond?

Yes. A jeweler uses a multi-tester, or a loupe to look for the doubled facet edges that only moissanite shows, and a gem lab can settle any doubt.

Why did a lab-grown diamond test as moissanite?

Many lab-grown diamonds grown under high pressure and high temperature contain traces of boron, which lets them conduct electricity. An electrical tester reads that as moissanite, even though the stone is a real diamond.

Does cubic zirconia pass a diamond tester?

No. Cubic zirconia conducts heat poorly, so even a basic thermal tester reads it as a simulant.

For the full comparison, read Moissanite vs Diamond, Moissanite vs Lab-Grown Diamond and Moissanite vs Cubic Zirconia.