October 04, 2026

Moissanite vs Diamond: How to Tell Them Apart, and Which Is Right for You

By Sasha Tarasova

Filed under Antique Diamonds & Diamond CutsAntique & Vintage Engagement RingsBuying Guides

Short answer: Moissanite is laboratory-grown silicon carbide, not a type of diamond. It is nearly as hard (9.25 on the Mohs scale against diamond's 10), shows noticeably more rainbow fire, and costs a small fraction of the price. The reliable way to tell moissanite from diamond is double refraction under a loupe, confirmed with a moissanite or multi-tester, because a basic thermal diamond tester reads moissanite as diamond.

We sell diamonds, mostly old ones, so you may expect us to be sniffy about moissanite. We are not. It is a legitimate material with real strengths. What we object to is confusion: moissanite sold as diamond, moissanite bought as an investment, and moissanite chosen by someone who would have been happier with something else. This guide is about seeing the difference clearly, in the stone and in the decision.

What is moissanite?

Moissanite is silicon carbide (SiC), a compound of silicon and carbon. The French chemist Henri Moissan identified natural silicon carbide in the 1890s in material from the Canyon Diablo meteorite site in Arizona, and at first believed he had found diamond. The mineral was named after him.

Natural moissanite occurs only as microscopic grains. Every moissanite in jewelry is manufactured. Colourless gem-quality moissanite reached the jewelry market in the late 1990s, and production has improved steadily since: early stones often carried a visible yellowish or greenish tint, while current production is sold in near-colourless grades.

Three definitions worth holding apart:

• Moissanite is a different material from diamond. It is not a "lab diamond".
• A lab-grown diamond is real diamond, carbon crystallised in the same cubic structure, made in a factory. Our guide to natural vs lab-grown diamonds covers that distinction.
• A simulant is anything that imitates diamond without being diamond: moissanite, cubic zirconia (CZ), white sapphire, glass.

Moissanite vs diamond: what is actually different?

The differences are physical and measurable. They are what every test in this article exploits.

Two terms deserve definitions. Refractive index measures how strongly a material bends light; higher usually means more brightness. Dispersion measures how strongly it splits white light into spectral colours; higher means more coloured flashes, which the trade calls fire. Moissanite has more than twice diamond's dispersion. That single number explains most of what you see.

How to tell moissanite from diamond

You can often suspect moissanite by eye and confirm it with a loupe. You should prove it with instruments.

1. Look at the fire

Moissanite throws strong rainbow colour, especially in daylight and under spotlights. A modern brilliant diamond shows fire too, but mixed with much more white light. When a stone looks like a disco ball, with most flashes coloured, moissanite is the first suspect. This is a clue, not proof: large, well-cut diamonds can be fiery, and antique cut diamonds sparkle differently, with broad flashes that include plenty of colour.

2. Look for doubled facet edges

This is the most reliable observation you can make yourself. Because moissanite is doubly refractive, each ray of light entering it splits in two. Under a 10x loupe, looking at an angle through the crown toward the back facets, the facet edges appear doubled, like a slightly out-of-register print.

The catch: cutters usually orient moissanite so that looking straight down through the table you are looking along the optic axis, the one direction in which no doubling appears. Tilt the stone and look through a side facet instead. Diamond, being singly refractive, never shows doubling from any direction.

3. Look at the inclusions

Moissanite often contains fine, straight, needle-like growth tubes running parallel to each other, and sometimes small reflective points. Natural diamond inclusions look different: small crystals, feathers (internal fractures), clouds and graining. Lab-grown diamonds have their own signatures. None of this is easy for a beginner, which is why the loupe is better at doubling than at inclusions.

4. Use the right tester

This is where most people go wrong. A basic diamond tester measures thermal conductivity, how fast heat moves through the stone. Diamond conducts heat extremely well. So does moissanite, close enough that most thermal testers read it as diamond.

A moissanite tester or multi-tester adds an electrical conductivity test. Moissanite conducts electricity; almost all diamonds do not. The exception is rare natural blue diamonds (type IIb), which contain boron and do conduct, so a multi-tester can flag a genuine blue diamond as moissanite. For a colourless stone, that exception rarely applies.

5. Weigh it, if it is loose

Moissanite is lighter than diamond for the same size: a moissanite with the same dimensions as a 1.00ct round diamond weighs roughly 0.9ct. That is why moissanite is usually sold by millimetre size or "diamond equivalent weight" rather than true carat weight. If a loose stone's measurements and weight do not match the diamond relationship, something is off.

6. Get a report

A gemmological laboratory identifies moissanite immediately and definitively. For any stone being bought or sold as diamond at a diamond price, that is the answer. Our guide to how to tell if a diamond is real covers the full range of tests, including the home myths that do not work.

Can a tester tell moissanite from a lab-grown diamond?

No, and this matters more every year. A lab-grown diamond is diamond. It passes thermal tests and moissanite tests exactly as a natural diamond does. Separating natural from lab-grown requires different equipment, typically spectroscopic screening devices or a laboratory. A store saying "we tested it, it's a diamond" is telling you it is not moissanite or CZ. It is not telling you the stone came out of the ground.

Is moissanite as durable as diamond?

Nearly. At 9.25 on the Mohs scale, moissanite is harder than every gemstone except diamond, including sapphire and ruby at 9. It resists scratching well, has good toughness, and lacks the pronounced cleavage planes along which a diamond can split from a hard, well-aimed knock. It will survive daily wear as an engagement ring. Our Mohs hardness guide puts the numbers in context: the scale is ordinal, so the gap between 9 and 10 is much bigger than the gap between 8 and 9.

Moissanite does not cloud or lose its sparkle over time from any change in the material. Like any stone, it gets dull when coated with skin oil and soap, and cleans up the same way.

How much does moissanite cost compared with diamond?

A fraction. Colourless moissanite typically costs a small percentage of what a natural diamond of similar size and appearance would cost, and meaningfully less than a lab-grown diamond. We will not quote figures; prices vary by brand, cut and grade, and have fallen over time. The structural point is simple: moissanite is a manufactured product, and its price reflects manufacturing costs and brand margin, not scarcity.

Does moissanite hold its value?

No. Buy moissanite because you like it, never as a store of value. The secondhand market is thin, and resale prices are typically a small portion of retail. The same logic applies, in a less extreme form, to lab-grown diamonds, where retail prices have fallen sharply as production scaled. Our honest look at whether lab-grown diamonds hold value explains the mechanics.

Natural diamonds are not an investment either, in the sense most people mean. But they do have an established secondhand market, and antique cut diamonds are a finite supply. That is a different proposition from a stone that can be manufactured in unlimited quantity next month.

Moissanite vs diamond: which is right for you?

An honest answer depends on what you value. There is no wrong choice, only a mismatch between the stone and the reason.

Moissanite makes sense if

• You want a large, bright, colourless look on a limited budget and do not care about resale.
• You like strong rainbow fire. Some people genuinely prefer it.
• You want a durable stone for travel or for a ring you will not worry about.

A diamond makes sense if

• You want the specific look of diamond, which is brighter and whiter in its sparkle and less rainbow.
• You care about the material's history, rarity or an established resale market.
• You are drawn to antique cuts. Moissanite is made in "old European" and "old mine" style cuts, but a replica cut does not have the soft, hand-cut character or the provenance of a real one, such as an old mine cut diamond set in a bezel of 18k gold.

The middle path people forget

An antique diamond is often less expensive than people assume, because antique cuts in warmer colours and lower clarity grades are priced very differently from modern stones. Before settling on moissanite for budget reasons, look at what a real old cut costs. Our guide to what $3k, $5k and $10k buy in an antique engagement ring and our old European cut price guide give the structure. You may still choose moissanite. At least you will be choosing it.

What should a seller disclose?

Everything. The FTC Guides for the Jewelry Industry (16 CFR Part 23) treat it as deceptive to describe a stone as a diamond when it is not, or to omit that a stone is laboratory-created. A moissanite ring should be described as moissanite, and a ring that combines moissanite side stones with a diamond centre should say so. In the secondhand market this breaks down more often than people think, usually through ignorance rather than fraud: a ring inherited, resold, and described as "diamond" because nobody tested it.

That is why we think a dealer should disclose how an identification was made, not just the result.

Moissanite in antique and vintage rings

This is the version of the problem that matters most to antique buyers. An original Edwardian or Art Deco mount has lost its centre diamond at some point, or had it sold, and a replacement went in. Since the late 1990s, that replacement is sometimes moissanite. The ring is genuinely old, the hallmarks are genuine, and the centre stone is not what the family story says it is.

Signs worth checking on any period ring:

• A modern cut in an old mount. A crisp modern round brilliant with a pointed culet, sitting in claws that were clearly re-tipped, is not proof of anything, but it tells you the stone may be a later replacement.
• Too much colour in the sparkle for a stone of that size and cut.
• Newer claw work around the centre than elsewhere on the ring, visible as brighter, less worn metal.
• Paperwork that describes the ring but not the stone, such as an old appraisal with no measurements.

A replacement stone does not make a ring worthless; it changes what the ring is and what it should cost. If there is a laboratory report, reading it properly will tell you whether its measurements match the stone in front of you.

Checklist: buying a secondhand "diamond" ring

1. Ask how the stone was identified, and with what equipment. "It tested as diamond" on a thermal tester alone does not exclude moissanite.
2. Look with a loupe through a side facet for doubled facet edges.
3. Notice the fire. Mostly rainbow flashes in a modern round is a reason to test further.
4. Check any report number against the laboratory's online verification, and compare the stated measurements to the stone.
5. For stones sold as natural, ask about lab-grown screening, not just simulant testing.
6. Get it in writing. The invoice should state the species and whether natural or laboratory-grown.

If you are weighing up the setting as well as the stone, our guide to choosing a vintage engagement ring covers what to check in the mount.

Questions people actually ask

Can a jeweler tell moissanite from a diamond?

Yes. A trained jeweler with a loupe will usually notice the doubled facet edges and strong rainbow fire of moissanite within a minute, and a moissanite tester or multi-tester confirms it by electrical conductivity. A jeweler relying only on an older thermal tester can be fooled, which is why the type of tester matters. A gemmological laboratory identifies moissanite with certainty.

Does moissanite pass a diamond tester?

Most basic thermal diamond testers read moissanite as diamond, because both conduct heat very efficiently. Moissanite testers and multi-testers add an electrical conductivity check, which moissanite fails because it conducts electricity. Rare natural blue diamonds also conduct, so a multi-tester can occasionally misread one of those as moissanite.

Is moissanite a fake diamond?

Moissanite is not diamond, but it is not fake either. It is a real material, silicon carbide, manufactured in a laboratory and sold under its own name. It becomes a fake diamond only when someone describes it as diamond. Sold honestly, it is a diamond alternative with its own properties, including more fire and slightly lower hardness.

Does moissanite get cloudy over time?

No. Moissanite does not change chemically or turn cloudy with age. What people notice is a film of skin oil, soap and lotion on the back of the stone, which dulls any gem, diamond included. Warm water, mild dish soap and a soft toothbrush restore it. Early moissanite from the late 1990s sometimes had a faint tint that owners mistake for clouding.

Is moissanite cheaper than a lab-grown diamond?

Generally yes, though the gap has narrowed as lab-grown diamond prices have fallen. Moissanite remains less expensive for the same visual size in most cases. Neither holds resale value well, so compare them on appearance and durability rather than on any expectation of getting money back later.

Why does my diamond show rainbow colours? Is it moissanite?

Not necessarily. All diamonds show fire, and antique cuts with high crowns and small tables can show broad, colourful flashes, particularly in warm or low light. The difference is proportion: moissanite shows much more colour relative to white light, and it shows doubled facet edges under a loupe. If in doubt, have it tested with a multi-tester or by a laboratory.

If you would rather find the real thing, a specific old cut diamond at a specific budget, our sourcing service runs that search for you. Or browse our antique and vintage engagement rings, and read more in the Journal's diamond guides.