Does Moissanite Pass a Diamond Tester? What Each Test Really Shows

It is one of the most searched questions about moissanite: will it pass a diamond tester? The short answer is that moissanite usually passes a basic thermal diamond tester, but it can be identified with a tester that also measures electrical conductivity, with a jeweler's loupe, or by a gem lab. Here is what each test actually measures, so you know what to expect.

First, a clear statement of how we work. Moissanite is a beautiful gem in its own right, and it is not a diamond. At Bhumi Gems we always describe and certify moissanite as moissanite. This guide is for curious owners and careful buyers, not for passing one stone off as another.

How a basic diamond tester works

The classic pen-style diamond tester measures thermal conductivity: how quickly heat moves through the stone. Diamond moves heat extremely well, far better than glass or cubic zirconia, so a thermal tester is a quick way to separate diamond from most look-alikes.

Moissanite also conducts heat very well, close to diamond. That is why a thermal-only tester will usually read moissanite as "diamond". When moissanite first reached the jewelry market in the late 1990s, this caught the trade by surprise and led to a new kind of tester.

Multi-testers and electrical conductivity

Most diamond testers sold today are multi-testers. Alongside heat, they check electrical conductivity. Almost all diamonds are electrical insulators, while moissanite conducts a small current, so a multi-tester will usually flag moissanite.

Two caveats are worth knowing:

• Some diamonds conduct electricity. Rare blue type IIb diamonds contain boron and are electrically conductive, so a multi-tester can mistake them for moissanite.
• Some moissanite conducts very little. Trade press reported in 2017 that some newer, whiter moissanite was so weakly conductive that older conductivity testers missed part of it. Testers that use ultraviolet light were promoted as a more reliable check for those stones.

In other words, a handheld tester gives a strong hint, not a final verdict.

The loupe test: double refraction

Moissanite is doubly refractive; diamond is singly refractive. When light enters moissanite it splits in two, so if you look through the side of the crown with a 10x loupe, the edges of the facets underneath can appear doubled, like a slightly blurred line drawn twice. Moissanite is usually cut so you see little doubling straight through the top, so tilt the stone and look at an angle. A trained jeweler can often spot moissanite this way in seconds.

Other clues

• Fire: moissanite throws noticeably more rainbow-colored flashes than diamond, especially in sunlight and in larger stones.
• Weight: moissanite is about 9 percent lighter than diamond for the same size, which a jeweler can measure on a loose stone.
• Gem lab: a gemological laboratory can identify moissanite with certainty using professional instruments.

What about lab grown diamonds?

A lab grown diamond is a real diamond, so it passes thermal and multi-testers as diamond. A standard handheld tester cannot tell a lab grown diamond from a mined one; that needs specialized laboratory equipment. If you are comparing the two stones, read Moissanite vs Lab Grown Diamonds.

Why this matters when you buy

• Always buy from a seller who states clearly whether a stone is moissanite, lab grown diamond or mined diamond.
• Keep your certificate or receipt. Every Bhumi Gems piece ships with a Bhumi Gems certificate of authenticity that states the stone and metal.
• If you ever resell, insure or have a ring appraised, expect the stone to be tested. Moissanite will be identified as moissanite, which is exactly as it should be.

Moissanite does not need to pretend to be anything else. At 9.25 on the Mohs scale, with more fire than diamond and a far lower price, it is a smart choice on its own merits. Explore our moissanite engagement rings or loose moissanite stones, or learn more in moissanite vs diamond.

Quick answers

Will moissanite pass a pen diamond tester?

A thermal-only pen tester will usually read moissanite as diamond. A multi-tester that also checks electrical conductivity will usually identify it as moissanite.

Can a jeweler tell moissanite from diamond?

Yes. With a multi-tester, a loupe to look for doubled facet edges, or a lab report, a jeweler can identify moissanite.

Is it a problem that moissanite tests as diamond on some testers?

Not if it is sold honestly. Moissanite should always be described as moissanite, and ours always is.