Quick Answer
Yes, moissanite can fool a basic diamond tester. But that’s not because moissanite “passed” as a diamond—it’s because the tester was asking the wrong question.
A standard diamond tester doesn’t test for “diamond.” It tests for thermal conductivity. And moissanite happens to be an excellent thermal conductor, just like diamond. So when the pen beeps, it’s not saying “this is a diamond.” It’s saying “this conducts heat quickly.”
The full truth: Modern multi-testers (which check both thermal and electrical conductivity) can reliably separate moissanite from diamond. Moissanite is electrically conductive; diamond is not. But some newer moissanite formulations have reduced conductivity so much that even these testers can be fooled .
Why the Confusion Exists
The diamond tester was invented as a shortcut. For decades, the main diamond simulant was cubic zirconia (CZ). CZ is a terrible thermal conductor. So a simple heat-based test was enough: if the stone conducts heat, it’s not CZ. If it doesn’t, it’s definitely not diamond .
Then moissanite entered the market. And moissanite conducts heat almost as well as diamond . Suddenly, the shortcut stopped working.
A thermal tester can no longer say “this isn’t a diamond.” It can only say “this isn’t CZ or glass.”
What a Basic Tester Actually Tells You
| Tester Result | What It Means | What It Doesn’t Mean |
|---|---|---|
| Beeps / Positive | The stone conducts heat well | It could be diamond, moissanite, or lab-grown diamond |
| No beep / Negative | The stone conducts heat poorly | It’s CZ, glass, or another common simulant |
A basic thermal tester is a screening tool for exclusion, not a confirmation tool . It’s great for quickly eliminating cheap fakes. It’s useless for proving “diamond.”
The Real Difference: Electrical Conductivity
The gemological solution to the moissanite problem was to add a second test: electrical conductivity .
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Diamond (natural and lab-grown): virtually non-conductive. (Rare exceptions exist, like blue Type IIb diamonds containing boron.)
So a multi-tester that checks both heat and electricity can reliably say:
This is the standard tool used by jewelers today.
The New Wrinkle: Forever One and Reduced Conductivity
In 2015, Charles & Colvard introduced Forever One, a higher-color moissanite with significantly reduced electrical conductivity. According to Sy Kessler, a leading tester manufacturer, the new material has “barely any” conductivity—so little that even electrical testers may read it as diamond .
This means the testing landscape is not static. Newer moissanite can sometimes pass even the multi-testers.
How to Actually Identify Moissanite (Without a Lab)
If you want certainty, the tester alone isn’t enough. Here’s what gemologists look for:
1. Double Refraction (The “Double Vision” Test)
Moissanite is birefringent—it splits light into two paths. Under a 10x loupe, you’ll see doubled facet edges or a “double vision” effect when looking through the stone. Diamond is singly refractive, so its facets are sharp and singular .
2. The Dot Test (for loose stones)
Place the stone table-down on a piece of paper with a dot. In a diamond, the dot is not visible through the pavilion. In moissanite, the dot may appear as a doubled or distorted image due to birefringence.
3. Specific Gravity
Moissanite has a specific gravity of 3.22; diamond is 3.52. In a heavy liquid like methylene iodide (SG 3.32), diamond sinks and moissanite floats .
4. Inclusions
Moissanite often contains fine, white, needle-like inclusions running in parallel lines. Diamond inclusions are entirely different .
What This Means for Moissanite as an Independent Gemstone
Here’s the part that rarely gets said:
Moissanite “passing” a diamond tester isn’t a problem to be fixed. It’s a fact to be understood.
The tester was designed before moissanite existed as a serious market presence. It was built to catch CZ. Moissanite simply happens to share one physical property with diamond—thermal conductivity—and that coincidence exposes the limitation of a one-dimensional test.
Moissanite doesn’t need to “pass” as a diamond. It needs to be recognized as what it is: a gemstone with its own measurable, distinct properties.
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Its electrical conductivity distinguishes it from diamond.
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Its double refraction creates a visual signature no diamond possesses.
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Its specific gravity and inclusions are diagnostic.
These aren’t flaws. They’re identity markers.
Frequently Asked Questions
Can moissanite pass a diamond tester?
A basic thermal tester: yes, often. A multi-tester (thermal + electrical): usually no, but some newer moissanite may still fool it .
Does passing a diamond tester mean moissanite is “fake”?
No. It means the tester is measuring one property (heat) and moissanite happens to share it. “Fake” is a category error. Moissanite is real moissanite.
Should I trust a diamond tester when buying jewelry?
For ruling out CZ and glass: yes. For confirming diamond: no. Always ask for a grading report from a reputable lab.
Why do some jewelers say moissanite is “not a real gemstone”?
That’s an outdated position. Moissanite has its own gemological parameters, a natural (if rare) origin, and a growing independent market. It’s a lab-grown gemstone, which is a legitimate category.
Final Thought
The diamond tester wasn’t designed to answer the question “Is this moissanite?” It was designed to answer “Is this worth selling as a diamond?”
Moissanite broke that question. Not because it’s a better diamond—but because it was never trying to be one.
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