How to Tell Moissanite from Diamond: 6 Checks That Work

Moissanite and diamond look alike at a glance, which is exactly why so many people choose moissanite. But they are different gemstones, and there are clear ways to tell them apart. Some checks you can do at home with a jeweler's loupe; others need a tester or a gem lab. Here is what each one shows, and how reliable it is.

1. Look for Rainbow Fire

Moissanite's dispersion is 0.104, more than twice diamond's 0.044. In practice that means more flashes of rainbow color, especially in direct sunlight or under spotlights, and more noticeable in stones over about 1 carat. A diamond sparkles too, but its light reads whiter, with more white "brilliance" and less colored fire.

How reliable: a good first hint, but not proof. Lighting, cut and stone size all change how much fire you see.

2. Check for Doubled Facets with a Loupe

This is the classic test. Moissanite is doubly refractive: light splits into two rays inside it. Diamond is singly refractive. With a 10x loupe, look through the stone from the side or at an angle toward the back facets. In moissanite, the facet edges often look doubled, like a slightly blurred double line. In diamond they look crisp and single.

Cutters orient moissanite so that the doubling is hard to see when you look straight down through the table, so tilt the stone and look at an angle. It is easiest to see in larger stones and in step cuts such as emerald.

How reliable: strong evidence when you can see it clearly. It takes a little practice.

3. Use the Right Kind of Tester

Many basic "diamond testers" measure how fast heat moves through a stone. Moissanite conducts heat much like diamond, so a thermal-only tester can read moissanite as diamond. Testers that also measure electrical conductivity can usually separate the two, because moissanite conducts electricity and most diamonds do not.

Even multi-testers are not perfect: the trade press has reported newer moissanite that some electrical testers missed. Rare natural blue diamonds also conduct electricity. We explain this in detail in does moissanite pass a diamond tester?

How reliable: a multi-tester is a useful screen; a thermal-only tester cannot tell moissanite from diamond.

4. Compare the Weight

Moissanite has a specific gravity of about 3.22, diamond about 3.52. So a loose moissanite is roughly 8 to 9 percent lighter than a diamond of exactly the same size and cut. A jeweler can measure a loose stone and compare its weight with what a diamond of that size should weigh.

How reliable: useful for loose stones only, and it needs an accurate scale and measurements.

5. Look at What Is Inside

Under magnification, moissanite can show thin needle-like inclusions that run parallel to each other, a feature of how the crystal grows. Natural diamonds more often show tiny crystals, feathers or clouds. Lab grown diamonds have their own growth features. Many moissanite and lab grown stones are so clean that there is little to see.

How reliable: a job for a trained gemologist, not a quick home test.

6. Ask a Gem Lab

A gemological laboratory can identify moissanite with certainty using instruments that measure how the stone handles light. If you need a definite answer, for insurance or resale, this is the way to get it.

What Does Not Work

• The fog test (breathing on the stone): both diamond and moissanite shed heat fast and clear quickly, so this does not separate them.
• The scratch test: both are very hard, and scratching a stone or another surface can damage your jewelry. Do not try it.
• The newspaper or dot test: it can help spot glass or cubic zirconia in a loose stone, but it is not a reliable way to tell moissanite from diamond, and it does not work on set stones.

Moissanite vs Diamond vs CZ at a Glance

Buying Moissanite with Confidence

At Bhumi Gems every moissanite piece is sold as moissanite, never as diamond, and every lab grown diamond is sold as a lab grown diamond. If you want to learn more about the stone itself, start with what is moissanite? or compare the two side by side in our moissanite vs diamond guide.

Ready to look? Browse moissanite engagement rings or loose moissanite stones.

Quick Answers

Can a jeweler tell moissanite from diamond?

Yes. With a loupe and a multi-tester, most jewelers can tell them apart quickly; a gem lab can confirm it with certainty.

Will moissanite pass a diamond tester?

It usually passes a thermal-only tester. A tester that also checks electrical conductivity will normally flag it as moissanite.

Can you tell moissanite from diamond with the naked eye?

Sometimes, by the extra rainbow fire in bright light. Most people cannot tell from normal viewing distance.

Is moissanite lighter than diamond?

Yes. It is roughly 8 to 9 percent lighter for the same size, which is why moissanite is often described by its size in millimetres.