Fake Diamonds vs Real Diamonds | Spot The Difference

If you have a stone and need to know whether it is real diamond or a simulant, the answer changes how much it is worth and how you should care for it. The good news: several simple at-home checks can get you most of the way there, and a jewelry store diamond tester finishes the job. Below are the real distinctions, the practical tests, and when it is worth visiting a jeweler.

What Makes A Diamond Real?

A real diamond — whether formed in the Earth’s mantle over millions of years or grown in a laboratory in a few weeks — is pure carbon arranged in a crystal lattice. It is the hardest natural substance on Earth, rating 10 on the Mohs scale. The Cape Town Diamond Museum explains that natural and lab-grown diamonds are “physically and chemically the same.”

Fake diamonds, technically called diamond simulants, are entirely different materials. The most common are cubic zirconia (zirconium dioxide), moissanite (silicon carbide), and occasionally white spinel (magnesium aluminum oxide) or simple glass. These imitate diamond’s sparkle but have lower hardness (8–9.25 Mohs), different density, and distinct internal structures.

At-Home Tests: What Works And What Can Damage Your Stone

The fog test is the safest first check: breathe on the stone the way you would fog a mirror. Real diamond disperses heat so quickly that the fog clears almost instantly; a simulant or glass will hold the fog for several seconds. Still, this is a screening test only — some moissanite can behave similarly to diamond on this check.

The water test works because diamond is dense at 3.51 g/cm³ and sinks in water. Drop a loose stone into a glass of water; if it floats or hovers rather than sinking, it is not diamond. This test is only for loose stones — mounted jewelry can trap air or be too light to sink regardless of the gem.

The newspaper or read-through test involves placing the stone upside down over small printed text. Diamond’s high refractive index bends light so sharply that you cannot read the text through it; if the letters are clearly legible, the stone is likely a simulant. Business Insider notes this is another method best tried on unmounted stones.

For a closer look, a 10x loupe reveals telling signs: real diamonds have sharp, crisp facet edges, natural inclusions (tiny internal marks), and seldom show scratches. Cubic zirconia often has rounded facet edges and may contain tiny bubbles; simulants scratch more easily than diamond. The Jewelers Mutual guide points to these visual cues as reliable indicators.

Lab-Grown Diamonds Are Real Diamonds

One common mistake people make: treating lab-grown diamonds as fake. Lab-grown diamonds have identical optical characteristics, same hardness, equal durability and longevity, and similar fire, brilliance, and sparkle as natural diamonds. The only difference is origin and price.

If you are considering a lab-grown diamond, it is still a real diamond. If you want a diamond simulant (a true fake diamond) for budget reasons or style preferences, our guide to the best fake diamonds covers the top simulant options worth your money.

The Most Reliable Final Check

No single at-home test is definitive. The fog test and water test are rough screenings; the loupe check is better but takes practice. For a certain answer, a diamond tester — available at many jewelry stores or as a handheld tool — measures thermal conductivity and distinguishes diamond from most simulants quickly and safely.

For the most reliable result, a professional jeweler can give you a confident verdict in minutes without risking damage to the stone or its setting. Scratch tests and heat tests are destructive and unnecessary; consumer guides widely recommend against them for mounted jewelry.