Yes, moissanite will usually pass a basic diamond tester. Those pens and probes measure heat transfer, and moissanite conducts heat so much like diamond that the device reads it as a diamond. Testers that also measure electrical conductivity, or use fluorescence spectroscopy, can tell the two apart. So the answer depends on the device in your hand, not on the stone alone.
This guide explains why that happens, which testers catch moissanite, what a “pass” does and does not prove, and how to check a stone at home without any gadget. We sell moissanite jewelry ourselves, so we say this plainly: a pass on a thermal tester is not proof that a stone is a diamond, and it is not a mark against moissanite either.
TL;DR
- Basic thermal diamond testers frequently read moissanite as diamond, because the two materials’ thermal properties are so close.
- Testers that add electrical conductivity, or that use fluorescence spectroscopy such as the GIA iD100, separate moissanite from diamond far more reliably.
- A pass only says “diamond-like thermal behavior”. Combine it with a loupe check for double refraction, and use a lab report for any high-value stone.
- Check certificate numbers on the issuer’s own website, never only on the inscription on the stone.
Table of Contents
- Why moissanite fools a basic diamond tester
- Which testers pass moissanite and which do not
- Why your stone might not behave as expected
- A pass is not an identification
- Check a stone at home without a tester
- Real moissanite vs fake: what the words really mean
- What the law says about naming these stones
- Our perspective on the “passes the tester” question
- When to see a gemologist
- Moissanite you can wear with confidence
- FAQ
- Sources
Why moissanite fools a basic diamond tester
A classic diamond tester is built to answer one question: is this cubic zirconia or something real? Cubic zirconia and glass hold heat. Diamond pulls heat away from the probe tip quickly, and the tester shows that as a pass.
Moissanite does the same thing almost as well. When synthetic moissanite reached the jewelry market in the late 1990s, gemologists writing in Gems & Gemology noted that its thermal properties are so close to those of diamond that the thermal probes on the market at the time reacted to it as if it were diamond. The testers had been designed to separate diamond from older simulants, and moissanite was simply not part of that design.
The U.S. Federal Trade Commission describes the same problem for consumers: thermal testers used to distinguish diamonds from cubic zirconia may not accurately identify moissanite, so the stone can falsely register as a diamond. Many of these older testers are still in circulation, in pawn shops, in market stalls and in drawers at home.
One detail worth knowing: some of these instruments are described as measuring thermal conductivity, but they actually measure thermal inertia of the material. That is a technical nuance, but it explains why two materials with different chemistry can give the same reading.
Which testers pass moissanite and which do not
Not all testers are equal. Here is how the common types behave, based on how each one works.
| Tester type | What it measures | Typical result on moissanite |
|---|---|---|
| Basic thermal pen or probe | Heat transfer | Often reads as diamond |
| Electrical conductivity (moissanite) tester | How the stone conducts electricity | Can separate moissanite from diamond |
| Combined thermal and electrical tester | Both properties | Designed to tell moissanite from diamond |
| Fluorescence spectroscopy device | Light response of the material | Does not rely on thermal properties |
| Laboratory analysis (for example Raman spectroscopy) | Molecular signature | Definitive when other tests are inconclusive |
The research behind this table is consistent. Modern devices distinguish moissanite by testing both electrical and thermal conductivity, or by using fluorescence spectroscopy. The GIA iD100, for example, gives a “Pass” for natural diamonds and “Refer” for stones that need more testing, in about two seconds. A moissanite would not be expected to get a simple pass there, and that is exactly the point of the design.
So if a jeweler in Zurich, Geneva or anywhere else tests your moissanite ring and it reads as a diamond, ask which kind of tester was used. If it was a basic thermal one, the result tells you very little.
Why your stone might not behave as expected
Readers often write that their stone passed once and failed on another day. A few ordinary reasons explain it:
- Different testers. A thermal pen and a combined tester will give different answers on the same stone. That is normal.
- Dirt and grease. A film of skin oil, lotion or soap residue on the surface can disturb a reading. Clean the stone before testing. If your moissanite looks dull, our guide on cloudy moissanite and a simple soapy-water fix covers the cleaning side.
- Metal contact. On a mounted stone, the probe may touch the setting. Place the tip on the stone itself, on a flat facet.
- A lab-grown diamond reading as moissanite. Readers also ask why a lab diamond tests as moissanite. That usually points to a tester or a stone problem worth rechecking with a better device, not to anything about the stone’s value. Take it to a gemologist.
A pass is not an identification
The most useful idea in this whole topic: a diamond tester does not identify a gemstone. It checks one property. Gemologists advise using multiple methods, because even newer testers can be tricked in unusual cases. GIA has documented synthetic moissanite coated with a thin diamond film, which is hard to identify because its luster and thermal properties correspond to diamond.
That is a rare case, mostly relevant to rough stones. But the lesson holds for everyone: one reading, from one device, should never decide a purchase or a resale price.
Check a stone at home without a tester
You do not need a device to tell moissanite from diamond. The most telling feature is optical, not thermal.
Moissanite is doubly refractive. Light entering the stone splits into two rays. GIA practitioners describe how, using a 10x loupe, you can see a doubling of the facet junctions, especially when looking through the side facets. Diamond is not doubly refractive, so its facet edges look single and crisp.
A simple routine:
- Clean the stone and let it dry.
- Use a 10x loupe in good, steady light.
- Tilt the stone and look through the side of the crown toward the opposite facets, not straight down through the table.
- Watch the back facet edges. If they appear doubled, you are looking at moissanite.
- Note the sparkle. Moissanite shows more flashes of rainbow color, which gemologists call dispersion or fire, than a diamond does.
We wrote a step-by-step version for buyers: 5 at-home checks to spot moissanite by double refraction. Practice on a stone you know is moissanite first, so you learn what doubling looks like before you judge another stone.
Real moissanite vs fake: what the words really mean
Readers type “real vs fake moissanite” and mean two different things.
Moissanite sold as moissanite is not fake. It is a genuine gemstone with its own properties. Lab-grown moissanite is real silicon carbide, made in a controlled process. It is not a diamond and does not claim to be one when sold honestly.
Fake moissanite is glass, cubic zirconia or another cheap material sold as moissanite. A fake will usually fail the double refraction check, and a good electrical tester will not mistake it for moissanite either. The simplest protection is to buy from a seller who states the material clearly and backs it with a report. Our article on whether buying moissanite online is safe and legitimate lists what to look for.
Moissanite passed off as diamond is the real fraud problem. GIA has reported a synthetic moissanite carrying a fraudulent GIA inscription, laser-marked on the girdle with a fake report number, so a buyer could think they were getting a natural diamond. The protection is simple: look the number up on the issuer’s own website, and do not trust the inscription alone. For the Swiss market, see our five-step moissanite certificate check.
What the law says about naming these stones
If you shop from U.S. sellers, note that the rules there are explicit. The FTC updated its Jewelry Guides in July 2018, and describing a simulated or laboratory-created stone simply as a diamond is considered deceptive. Marketers must disclose the nature of the stone clearly, immediately before the word “diamond”. In 2019 the agency sent warning letters to companies over diamond ad disclosures.
That is a U.S. rule. Swiss and EU rules differ, so if you buy in Switzerland, ask the seller in writing what the stone is and what documents come with it. Honest sellers answer that question in one line.
Our perspective on the “passes the tester” question
We see this keyword as a sign of a deeper worry: “Will I be sure what I own?” That worry is fair, and we would rather answer it than dodge it.
Moissanite passing a basic tester is sometimes used as a selling point. We do not use it that way. A moissanite does not need to imitate a diamond to be worth wearing. It has its own character: strong fire, high hardness, and a price that lets you buy a larger statement piece without a large budget. GIA’s own framing is that moissanite is a distinct gemstone with its own properties rather than only a diamond substitute, and we agree with it.
Our customers are mostly women who want pieces that look striking at work and at dinner, who care where a stone comes from, and who do not want to pay for a name. For them, the right question is not whether the stone fools a device. It is whether the stone is described honestly, whether it is made well, and whether the maker stands behind it.
So here is how we think about it:
- We call our stones lab-grown moissanite, every time.
- We would want you to test them with a loupe, and we wrote the guide to help you do it.
- We back our jewelry with a lifetime warranty, and 100% of our profits go back to the people who make it.
- If you ever need to know for certain what a stone is, a gemological lab is the answer, for ours or anyone’s.
Whether moissanite suits an engagement ring is a separate question, which we cover in our look at value, ethics and warranty, and how well it holds up to daily wear.
— Ammar
When to see a gemologist
Home checks are good for curiosity and for screening. Go to a professional when:
- you are buying or selling a stone that costs a significant amount;
- the stone is loose and unmarked, or from an unknown seller;
- a tester result and a loupe result disagree;
- a stone arrives with a report you cannot verify.
Gemologists point out that professional laboratory verification remains the most reliable way to confirm any high-value gemstone, and that Raman spectroscopy is the definitive method when other tests do not settle it. In Switzerland, ask a jeweler or an accredited gem lab what instruments they use before you pay for a test.
Moissanite you can wear with confidence
If you like the idea of a stone with serious sparkle, honest labeling and an ethical story, our collection is built around lab-grown moissanite: rings, necklaces, bracelets, earrings and stacking sets. You can start with women’s rings, browse tennis bracelets, or see everything on the Meri Jaan home page. Club members also get unlimited exchanges.
FAQ
Does moissanite pass a diamond tester?
On a basic thermal tester, usually yes, because moissanite’s thermal behavior is very close to diamond’s. On a tester that also checks electrical conductivity, or on a fluorescence spectroscopy device, it should be identified as something other than a natural diamond.
Which diamond tester can detect moissanite?
Look for a combined thermal and electrical tester, or a device that uses fluorescence spectroscopy, such as the GIA iD100. For a definitive answer on a valuable stone, a lab using Raman spectroscopy is the gold standard.
How can I test my moissanite at home?
Use a 10x loupe and look through the side facets for doubled facet junctions, which show double refraction. Clean the stone first and compare against a stone you know is moissanite. Our at-home double refraction guide walks through it.
Can a diamond tester be fooled?
Yes. Basic thermal testers are fooled by moissanite, and GIA has documented a case of moissanite coated with a thin diamond film that is hard to identify. That is why gemologists combine several methods.
Is moissanite a fake diamond?
No. It is a different gemstone with its own properties, including higher dispersion and double refraction. It is only a problem when a seller presents it as a diamond, which is deceptive under U.S. FTC guidance.
Sources
- Synthetic Moissanite: A New Diamond Substitute, Gems & Gemology
- The GEM DiamondMaster and the Thermal Properties of Gems, Gems & Gemology
- In the Loupe: Advertising Diamond, Gemstones and Pearls, FTC
- GIA iD100 Gem Testing Device
- Synthetic Moissanite Coated with Diamond Film Imitating Rough Diamond, Gems & Gemology
- Synthetic Moissanite with Fraudulent GIA Inscription, Gems & Gemology
- Jewelry Guides, FTC
- FTC Sends Warning Letters Regarding Diamond Ad Disclosures
- GIA
