Here’s the honest, complete answer: it depends entirely on the type of tester. On a standard thermal diamond tester, moissanite usually does pass as diamond because moissanite conducts heat similarly to a real diamond. But on a modern dual tester that also checks electrical conductivity, moissanite is correctly identified as moissanite because it conducts electricity while diamond does not. So “does moissanite pass a diamond tester” has two answers depending on the equipment, and understanding why reveals something important: moissanite isn’t a sneaky diamond imitation; it’s a distinct gemstone with its own properties. Here’s the full explanation and how the stones are actually told apart.
The Short Answer, Two Ways
On a basic thermal diamond tester:
Yes, moissanite usually passes as diamond. These common, inexpensive testers work by measuring how quickly a stone conducts heat. Both diamond and moissanite conduct heat very efficiently, so a thermal tester often reads moissanite as diamond. This is the origin of the widespread belief that “moissanite fools diamond testers.”
On a modern dual tester (thermal plus electrical):
No, moissanite is correctly identified. Newer testers measure both heat conductivity and electrical conductivity. Here’s the key difference: moissanite conducts electricity, while diamond does not. So a dual tester detects that electrical conductivity and flags the stone as moissanite rather than diamond.
The bottom line is that whether moissanite “passes” depends entirely on which tester is used. An older thermal-only tester can be fooled; a modern dual tester cannot. Most reputable jewelers today use dual testers precisely because thermal-only testers can’t distinguish moissanite from diamond.
Why Moissanite Passes Thermal Testers (The Science)
To understand why moissanite behaves the way it does with diamond testers, it helps to understand what the testers actually measure and why these two stones respond differently.
A thermal diamond tester works on a simple principle: diamond conducts heat exceptionally well, better than almost any other material. The tester applies a tiny amount of heat to the stone and measures how quickly that heat disperses. A real diamond disperses heat rapidly, giving a positive “diamond” reading. Most diamond simulants, like cubic zirconia, conduct heat poorly, so they fail this test, which is exactly what a thermal tester is designed to catch.
Moissanite is the exception. Moissanite, made of silicon carbide, also conducts heat very efficiently, nearly as well as diamond. So when a thermal tester is applied to moissanite, the heat disperses quickly, just as it would with a diamond, and the tester reads it as diamond. This isn’t a flaw or a trick; it’s simply that moissanite genuinely shares this one property with diamond.
This is why thermal testers, which are excellent at catching cheap simulants like cubic zirconia, cannot catch moissanite. Moissanite’s high thermal conductivity is real, and it’s the reason the “moissanite passes diamond testers” fact became so widely known.
Why Dual Testers Catch Moissanite (The Key Difference)
The limitation of thermal testers created a need for a better tool, and the solution came from a property where diamond and moissanite genuinely differ: electrical conductivity.
Diamond is an excellent thermal conductor but an electrical insulator; it does not conduct electricity. Moissanite, on the other hand, conducts both heat and electricity. This single difference is what modern testers exploit.
A dual tester (also called a moissanite tester or a combination tester) measures both properties. First, it checks thermal conductivity, which both diamond and moissanite pass. Then it checks electrical conductivity. A diamond shows no electrical conductivity and is confirmed as diamond. Moissanite shows electrical conductivity and is flagged as moissanite. Because the two stones differ reliably on this property, a dual tester distinguishes them accurately every time.
This is why the moissanite-fools-testers concern is largely outdated for anyone using current equipment. Dual testers are now standard, affordable, and widely used by jewelers, so moissanite is readily identified in any professional setting. The idea that moissanite can secretly pass as diamond belongs to the era of thermal-only testers.
For more on why diamonds conduct heat but not electricity, which comes down to their pure carbon crystal structure, see our guide on what lab grown diamonds are made of.
How to Tell Moissanite From Diamond (Beyond Testers)
Diamond testers aren’t the only way to distinguish the two stones. Because moissanite and diamond are genuinely different materials, there are several ways to tell them apart, some you can even observe yourself.
Double refraction (the most reliable visual cue). This is the clearest way to spot moissanite by eye or with a loupe. Moissanite is doubly refractive, meaning it bends light twice as it passes through, which creates a slight “doubling” of the facet edges when you look through the stone. Diamond is singly refractive and shows no such doubling. In larger moissanite stones especially, viewing through the top at an angle can reveal this doubled appearance. Diamonds never show it.
Fire and sparkle. Moissanite has more fire, more colorful, rainbow-like flashes, than diamond because it has a higher dispersion. Under bright light, moissanite throws noticeably more colored light than a diamond, which has a more balanced mix of white and colored sparkle. To a trained eye, moissanite’s extra fire is a giveaway, though to a casual observer the stones can look similar.
A dual diamond tester. As covered above, a modern dual tester instantly and reliably distinguishes the two by checking electrical conductivity. This is the definitive quick method and what jewelers use.
Professional examination. A gemologist can identify moissanite conclusively using magnification and specialized equipment, observing the double refraction, inclusions characteristic of moissanite, and other properties. For absolute certainty, professional examination is definitive.
The takeaway is that while moissanite can fool an old thermal tester, it’s genuinely easy to identify through double refraction, its extra fire, a dual tester, or professional examination. The two stones are distinguishable as they’re different materials, and anyone who needs to know which is which can find out readily.
Moissanite Isn’t a Diamond Fake, It’s Its Own Stone
Here’s the honest, important point that the whole tester question leads to: the fact that moissanite shares one property with diamond (thermal conductivity) doesn’t make it a diamond imitation or a trick. Moissanite is a genuine, distinct gemstone with its own real properties, some of which happen to overlap with diamond and some of which clearly don’t.
This matters because the “does it pass a diamond tester” question is sometimes framed as if moissanite is trying to sneak past as a diamond. It isn’t. Moissanite (silicon carbide) is a legitimate gemstone valued in its own right, for its exceptional brilliance, its fire, its durability, and its beauty. It’s not sold as a secret diamond substitute; it’s sold openly as moissanite, a stone many people genuinely prefer.
At EthicStone, we sell moissanite transparently as moissanite, never disguised as anything else, because it’s a beautiful, durable, ethical stone that stands on its own merits. Whether a particular tester reads it as diamond or correctly identifies it as moissanite doesn’t change what it is: a distinct, legitimate gemstone. If you want to understand how moissanite compares to a lab grown diamond, our moissanite vs lab grown diamond guide covers the differences in full, and our moissanite vs cubic zirconia guide explains why moissanite is far superior to the cheap simulant that thermal testers do catch.
Common Things People Get Wrong About Moissanite and Diamond Testers
- Moissanite always passes as diamond on any tester. False. Moissanite passes basic thermal testers but is correctly identified by modern dual testers that check electrical conductivity. Whether it “passes” depends entirely on the type of tester used.
- If moissanite passes a diamond tester, it must be a diamond. No. Passing a thermal tester only means the stone conducts heat well, which moissanite does. It doesn’t make moissanite a diamond. The two are different materials, and a dual tester or double refraction will reveal the difference.
- Moissanite is designed to fool people into thinking it’s a diamond. Untrue. Moissanite is a legitimate gemstone sold openly on its own merits. The fact that it shares thermal conductivity with diamond is a natural property, not a deception. Reputable sellers sell moissanite as moissanite.
- You can’t tell moissanite from diamond at all. False. Moissanite is readily distinguished by its double refraction (visible doubling of facets), its extra fire, a dual tester, or professional examination. It only fools outdated thermal-only testers, not the eye of anyone who knows what to look for or modern equipment.
- Cubic zirconia and moissanite both pass diamond testers. Only partly, and differently. Cubic zirconia fails thermal testers because it conducts heat poorly, which is exactly what those testers catch. Moissanite passes thermal testers because it conducts heat well. They behave oppositely on a thermal tester.
Frequently Asked Questions
⮞ Does moissanite pass a diamond tester?
It depends on the tester. On a basic thermal diamond tester, moissanite usually passes as diamond because it conducts heat similarly to diamond. On a modern dual tester that also measures electrical conductivity, moissanite is correctly identified as moissanite because it conducts electricity while diamond does not.
⮞ Why does moissanite pass a thermal diamond tester?
Moissanite passes thermal testers because it conducts heat very efficiently, nearly as well as diamond. Thermal testers work by measuring how quickly a stone disperses heat, and since moissanite disperses heat rapidly like a diamond, the tester reads it as diamond. This is a real shared property, not a trick.
⮞ How do you tell moissanite from a diamond?
The most reliable visual method is double refraction: moissanite bends light twice, creating a slight doubling of facet edges, while diamond does not. Moissanite also has more fire (rainbow flashes) than diamond. A dual diamond tester or professional gemological examination will identify the two definitively.
⮞ Will moissanite fail a diamond tester?
On a thermal-only tester, moissanite usually will not fail, as it passes as diamond. On a dual tester that checks electrical conductivity, moissanite is correctly flagged as moissanite rather than passing as diamond. So whether it “fails” depends on the tester: thermal-only testers can’t catch it as dual testers can.
⮞ Can jewelers tell moissanite from diamond?
Yes, easily. Jewelers use dual testers that check electrical conductivity to distinguish moissanite from diamond reliably, and they can also observe moissanite’s double refraction and extra fire under magnification. Any reputable jeweler can identify moissanite quickly and definitively with standard modern equipment.
⮞ What’s the difference between a diamond tester and a moissanite tester?
A basic diamond tester measures only thermal conductivity, which both diamond and moissanite pass, so it can’t tell them apart. A moissanite tester (or dual tester) also measures electrical conductivity. Since moissanite conducts electricity and diamond doesn’t, the dual tester distinguishes them accurately.
⮞ Does cubic zirconia pass a diamond tester?
No. Cubic zirconia conducts heat poorly, so it fails thermal diamond testers, which is exactly what those testers are designed to catch. This is the opposite of moissanite, which passes thermal testers because it conducts heat well. The two simulants behave oppositely on a thermal tester.
⮞ Is moissanite a real gemstone or a fake diamond?
Moissanite is a real, distinct gemstone made of silicon carbide, not a fake diamond. It’s valued in its own right for its brilliance, fire, and durability, and it’s sold openly as moissanite. Sharing thermal conductivity with diamond doesn’t make it a diamond or an imitation, as it’s simply a natural property of the stone.
⮞ Does moissanite conduct electricity?
Yes. Moissanite conducts both heat and electricity, while diamond conducts heat but not electricity. This difference in electrical conductivity is exactly what modern dual testers use to distinguish moissanite from diamond, since diamond is an electrical insulator and moissanite is not.
⮞ Can you see the difference between moissanite and diamond with the naked eye?
To a casual observer, moissanite and diamond can look similar, especially in smaller stones. However, moissanite’s extra fire (more rainbow flashes) and, in larger stones, its double refraction (doubled facet edges viewed at an angle) can reveal the difference. A trained eye can often tell them apart; most people cannot without looking closely.
So, does moissanite pass a diamond tester? The honest answer is that it depends on the tester: moissanite passes basic thermal testers because it conducts heat like a diamond, but modern dual testers correctly identify it by detecting the electrical conductivity that diamond lacks. The old belief that moissanite secretly fools all diamond testers belongs to the era before dual testers became standard.
More importantly, the whole question reveals that moissanite isn’t a diamond imitation trying to pass as something it’s not. It’s a genuine, distinct gemstone with its own real properties, readily identifiable through double refraction, its extra fire, a dual tester, or professional examination, and valued in its own right. Whether a tester reads it as diamond or correctly identifies it as moissanite doesn’t change what it is: a beautiful, durable, legitimate stone.
Explore our moissanite engagement rings to see moissanite’s beauty for yourself, or compare it to other stones in our moissanite vs. lab-grown diamond guide.