Why Does Moissanite Pass a Diamond Tester? Thermal Conductivity Explained

September 7, 2026

If you're considering buying a moissanite ring — or if you already own one — you've probably encountered the question: does moissanite pass a diamond tester? The answer is yes, and understanding why reveals something genuinely fascinating about the physics of this gemstone.

What Diamond Testers Actually Measure

Most diamond testers sold online and used by jewelers measure thermal conductivity — how quickly heat passes through a material. The tester applies a small, controlled heat source to the stone's surface and measures how fast that heat dissipates through the gem.

Diamond has extraordinarily high thermal conductivity: approximately 900–2,320 W/m·K depending on the type. This is dramatically higher than glass (1 W/m·K), cubic zirconia (CZ, ~2 W/m·K), and most other gemstones. Traditional diamond testers are calibrated to detect this specific thermal property — if a stone conducts heat like a diamond, the tester reads positive.

Moissanite's thermal conductivity is 490–490 W/m·K — lower than diamond, but dramatically higher than CZ, glass, and most simulants. This is high enough that older-generation thermal testers read moissanite as diamond.

Why This Matters for Buyers

For buyers, this is actually reassuring rather than alarming. Moissanite's high thermal conductivity is a property of its crystalline structure — silicon carbide — not a manufacturing trick or a coating. It is intrinsic to the material.

This means moissanite is the only diamond simulant that:

Passes thermal conductivity diamond tests
Has a hardness (9.25 Mohs) close to diamond (10 Mohs)
Has a refractive index (2.65–2.69) that exceeds diamond (2.42)
Is chemically stable over decades of daily wear

No other simulant — not CZ, not white sapphire, not glass — comes close to this combination of physical properties. This is why moissanite is classified as a fine gemstone, not a fashion stone.

Modern Diamond Testers: The Moissanite-Specific Test

Jewelers and gemologists who work with both diamonds and moissanite regularly use dual-mode testers that measure both thermal conductivity and electrical conductivity. Moissanite is a semiconductor — it conducts small amounts of electricity in a way that diamond does not. This electrical conductivity test reliably distinguishes moissanite from diamond.

These dual testers are widely available and inexpensive. Any jeweler who tests gemstones professionally will use one. If you ever need to have your stone tested, this is the appropriate tool — and a knowledgeable jeweler will use it correctly.

Should This Change Your Buying Decision?

No. The fact that moissanite passes thermal diamond tests is a consequence of its genuine physical properties, not a scam or a deception. Moissanite is sold as moissanite — not as diamond. Its GRA certificate identifies it clearly as silicon carbide moissanite, with its color, clarity, and carat weight graded independently.

The combination of high thermal conductivity, extreme hardness, and superior brilliance makes moissanite the most credible diamond alternative available. These are not marketing claims — they are measurable physical properties documented in gemological science.

How to Verify Your Moissanite

Every Moissanite Shine stone comes with a GRA (Gemological Research Association) certificate that independently verifies your stone's identity, color grade, clarity grade, and carat weight. You can verify your certificate number directly with GRA. This is the standard of transparency we hold ourselves to on every stone we sell.

Read our detailed guide: How to Verify Your Moissanite Certificate.

Ready to choose your stone? Explore our engagement ring collection — all DEF color, VVS1 clarity, GRA-certified — or browse our best-selling jewelry.

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