Quick answer: The fastest reliable way to tell moissanite from diamond is a moissanite tester that measures electrical conductivity, because a standard thermal diamond tester will wrongly read moissanite as diamond. Visually, moissanite shows more rainbow fire and often a slight double-refraction (doubling of facet edges under magnification) that diamond never shows. For any purchase or resale, confirm with an instrument rather than the eye alone.
What is moissanite?
Moissanite is a lab-created gemstone made of silicon carbide. It is nearly as hard as diamond, brilliant, and far cheaper, which makes it a popular diamond alternative. Because it looks so close to diamond, it is also the simulant most likely to fool a quick visual check or a basic thermal tester.
Key differences between moissanite and diamond
Fire and brilliance: Moissanite disperses light into more coloured flashes, giving a stronger rainbow effect. Diamond shows a more balanced mix of white and coloured sparkle.
Double refraction: Moissanite is doubly refractive. Under 10x magnification you can often see facet edges appear doubled. Diamond is singly refractive and never doubles.
Hardness: Diamond is 10 on the Mohs scale; moissanite is about 9.25. Both are durable, but diamond is the hardest.
Conductivity: Both conduct heat, which is why thermal-only testers fail. Moissanite conducts electricity, so an electrical-conductivity probe separates them instantly.
Price and origin: Moissanite is lab-made and costs a fraction of diamond, which is why accurate identification protects your money.
How to test moissanite vs diamond reliably
Use a combination tester with a moissanite or electrical-conductivity function; a thermal-only pen is not enough. Examine the stone at 10x with a loupe or microscope for doubling of facet edges. For loose stones, a refractometer will show moissanite's higher, doubled refractive index. When value is significant, confirm with more than one method.
Frequently asked questions
Can a diamond tester detect moissanite? Only if it has a moissanite or electrical-conductivity function. A thermal-only diamond tester will read moissanite as diamond, so use a combination tester.
How can I tell moissanite from diamond at home? Look for extra rainbow fire and, under a 10x loupe, doubled facet edges. These hints suggest moissanite, but only an electrical-conductivity tester confirms it.
Is moissanite a real diamond? No. Moissanite is silicon carbide, a separate lab-created gemstone. It is a diamond simulant, not a diamond.
Does moissanite pass a diamond tester? On a thermal-only tester, yes, it can pass as diamond. On a combination tester with moissanite detection, it is correctly identified.
Why does moissanite sparkle more than diamond? Moissanite has higher dispersion, so it splits light into more coloured flashes. Some buyers like this; others prefer diamond's balanced sparkle.
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