Diamond vs Moissanite vs CZ: How to Tell the Difference
Why This Comparison Matters
Diamond, moissanite, and cubic zirconia (CZ) are the three stones most commonly confused with one another. They can look nearly identical in a finished piece of jewelry, yet they differ dramatically in hardness, thermal conductivity, refractive index, and market value. Whether you're a jeweler, appraiser, or informed buyer, knowing how to distinguish them is essential.
At a Glance: Key Properties Compared
| Property | Diamond | Moissanite | Cubic Zirconia |
|---|---|---|---|
| Hardness (Mohs) | 10 | 9.25 | 8–8.5 |
| Refractive Index | 2.42 | 2.65–2.69 | 2.15–2.18 |
| Thermal Conductivity | Very high | High (near diamond) | Low |
| Electrical Conductivity | None | Yes | None |
| Density (g/cm³) | 3.52 | 3.21 | 5.6–6.0 |
| Dispersion (fire) | 0.044 | 0.104 | 0.060 |
| Origin | Natural or lab-grown | Lab-grown | Lab-grown |
| Relative cost | High | Medium | Low |
Visual Differences
Brilliance and Fire
Moissanite has a higher refractive index than diamond and significantly more dispersion ("fire"). Under bright light, moissanite produces a rainbow-like sparkle that experienced jewelers describe as "disco ball" effect — beautiful, but distinctly different from diamond's crisp white brilliance. CZ has less fire than both and tends to look glassier over time as it accumulates surface scratches.
Colour
High-quality CZ is often perfectly colourless — sometimes more so than a natural diamond. Moissanite can show a faint yellow or green tint in certain lighting, particularly in larger stones. Natural diamonds range from colourless (D) to light yellow (Z) on the GIA scale.
Wear Over Time
Diamond's hardness of 10 means it resists scratching indefinitely. Moissanite (9.25) holds up very well in daily wear. CZ (8–8.5) will show surface abrasion within months of regular wear, dulling its initial brilliance.
How Professional Testers Distinguish Them
Thermal Tester Alone: Not Enough
A standard thermal conductivity tester will read both diamond and moissanite as "diamond" — because moissanite's thermal conductivity is close enough to trigger a positive result. This is the most common source of misidentification in the field.
Dual Thermal-Electrical Tester: The Definitive Tool
Moissanite conducts electricity; diamond does not. A dual-mode tester measures both thermal and electrical conductivity simultaneously, producing a clear three-way result: diamond, moissanite, or simulant (CZ/glass). This is the professional standard for rapid, non-destructive identification.
→ GemTrue's Multi Plus Diamond Tester and the Diamond Experior are designed for exactly this scenario — delivering definitive diamond vs moissanite vs CZ results in seconds.
Loupe Inspection
Under 10× magnification, moissanite often shows doubling of the back facets — a phenomenon caused by its double refraction (birefringence). Diamond is singly refractive and shows no such doubling. CZ is also singly refractive but typically flawless, with no inclusions.
→ The GemTrue All-Seeing Eye 10x Loupe is an essential companion to any electronic tester for visual confirmation.
UV Fluorescence
Under longwave UV, many diamonds fluoresce blue. Moissanite typically fluoresces a different colour or not at all. CZ may show orange or yellow fluorescence. This is a supporting test, not a standalone identifier.
Which Stone Is Right for Which Purpose?
This is not a question of "real vs fake" — it's a question of informed choice. Moissanite is a legitimate, durable gemstone with its own market. CZ is a cost-effective simulant widely used in fashion jewelry. The issue arises only when one stone is misrepresented as another.
For professionals handling estate pieces, pre-owned jewelry, or loose stones, a dual-mode tester and a quality loupe are the minimum toolkit for accurate identification.
Frequently Asked Questions
Can a jeweler tell moissanite from diamond by eye?
An experienced jeweler may suspect moissanite based on its distinctive fire and facet doubling under a loupe, but electronic testing is required for certainty.
Is moissanite a fake diamond?
No. Moissanite is a distinct gemstone (silicon carbide) with its own properties and value. It is not a diamond simulant in the same category as CZ — it simply looks similar and is sometimes sold as a diamond alternative.
Does CZ pass a diamond tester?
No. CZ has low thermal conductivity and will read as a non-diamond on any standard thermal tester. It is the easiest of the three to identify electronically.
How can I tell if my engagement ring stone is diamond or moissanite?
The most reliable method is a dual thermal-electrical tester. If you don't have one, a jeweler can test it in minutes. Look also for facet doubling under a loupe — a strong indicator of moissanite.
Let customers speak for us
The best loupe ive ever had
Great device to look at the inscription of loose diamonds and also diamond jewelry.
Much simpler to operate, can’t beat the price. Excellent tester.
I have begun using the cell on a gemmological stereo microscope, and the immersion cell sits on the 'ledge' above the adjustable iris diaphragm with a very small amount of wiggle room - this does not appear to be raising any issues. The microscope filter and Immersion cell combo is a well-constructed unit of good size which makes it more stable whilst maneuvering the gemstone with tweezers. The same can be said for adjustment the required light source/s on the gemstone and the white diffuser is easily placed under the cell. Thus, the gemstone inclusions are easier to bring into focus to observe.
I am extremely happy with this Diamond Selector Kit.
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The quality and overall presentation are absolutely beautiful and very professional.
The kit looks elegant, feels high-end and is perfect for jewelry consultations. It helps customers visualize different diamond sizes and shapes directly on the hand, which makes the consultation process much easier and more enjoyable.
I am especially impressed by the optical appearance and the high-quality execution of the entire set.
I am very glad that I decided to purchase this premium selector kit.
I also want to mention the excellent customer service.
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Excellent product and highly recommended!
Everything was beautiful! And great service!! Thank you so much.
This is a great piece of kit, My Veritas has already paid for itself by testing over $1200 worth of purchased IGI Lab created diamonds that were proven to be Moissanite with fake certificates and have been returned for full refunds, Many thanks for the life saver GemTrue
The tool is very impressive and highly practical. It can be used to examine both rings and loose stones, including diamonds, zircons, and any round-cut gemstone. The rotating bottom disc allows for a smooth 360-degree view, which makes inspections much easier.
One suggestion for improvement would be to offer an optional ring holder attachment for examining single stones more conveniently. Another enhancement could be integrating a built-in light source, which would greatly improve visibility in low-light conditions.
The main idea behind this tool is to simplify the process of reading serial numbers and matching them with certificates. It also provides an excellent, clear view of the girdle area, making it a valuable addition to any gemologist’s toolkit.
I use a loupe daily, sometimes in proper light, many times not. Having a light is attached and not interfering is awesome. Having lwuv also great when viewing pearls. More importantly rechargeable makes it easy. 5 stars
Very nice lens! Rechargeable light is very convenient! I have used it several times in the fees days that I have had it and have been very pleased!
I had a less accurate probe that told me the moissanite was a cvd/hpht diamond. that will be going back for a refund . this tester DK10100 what you got no BS. I love it ,had to pay the price but in the end it will save time and money.
This loupe is perfect for inspecting diamonds and moissanite in low-light settings. The LED light makes it much easier to see details clearly. It’s compact and fits right in my pocket, making it super convenient to carry around.
I use this set in my jewelry business to show clients various diamond shapes and sizes. The diamonds and moissanite are high quality, and the case is perfect for keeping everything organized.
This tester is excellent for professionals like me who work with various diamonds and moissanite. It’s precise and fast, and the combo set with the thermal tester is perfect for all my needs.
The tester is lightweight and works great! It gives quick and accurate results, and the UV light feature is a nice touch for fluorescence testing.
