How to Tell If a Diamond Is Real
A few quick at-home checks can rule out glass and cubic zirconia, and a photo of the stone and its setting stamps tells you a lot more. Upload one and our free AI reads the clues in seconds.
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How to Identify Is My Diamond Real?
Check these features before you rely on any single one — the combination is what confirms the ID.
Breathe on the stone like you're fogging a mirror. A diamond disperses heat fast, so the fog clears almost instantly; on glass or cubic zirconia it lingers for a few seconds. Moissanite also clears fast, so passing doesn't prove it's a diamond.
Diamonds return bright white light (brilliance) with flashes of color. Cubic zirconia throws an excessive, oily rainbow of color, and moissanite shows strong 'disco ball' rainbow flashes, especially in sunlight.
With a 10x jeweler's loupe, real diamonds usually show tiny natural inclusions and crisp, sharp facet edges. Glass shows rounded, chipped edges and sometimes air bubbles. A flawless-looking large stone deserves a lab check.
Look at the back facets through the top at a slight angle. If the facet edges look doubled or blurry, the stone is doubly refractive, which points to moissanite rather than diamond.
Check the inside of the band. Real diamonds are usually set in gold or platinum stamped 10K, 14K, 18K, PT, or 950. A '925' sterling or 'C.Z.' stamp suggests a simulant, though stamps aren't proof either way.
Many certified diamonds have a tiny report number laser-inscribed on the girdle (the thin outer edge), visible with a loupe. Match it with a GIA or IGI grading report to confirm the stone.
Diamond Simulants and How to Spot Them
Natural Diamond
Clears fog instantly, white brilliance with moderate fire, sharp facet edges, often tiny inclusions under a loupe, usually in a gold or platinum setting.
Lab-Grown Diamond
A real diamond, chemically and physically identical to a mined one, so it passes every home test and standard diamond tester. Only a gem lab can tell them apart; many are laser-inscribed 'lab grown'.
Moissanite
Very hard and passes the fog test and thermal 'diamond testers'. Shows strong rainbow flashes and doubled facet lines. A multi-tester that checks electrical conductivity can tell it apart.
Cubic Zirconia (CZ)
Heavier than diamond, fog lingers, very colorful 'fire', and edges wear and scratch over time. Often set in sterling silver.
Glass / Crystal
Fog lingers, facet edges are rounded or chipped, may contain bubbles, and it scratches easily. Common in costume and vintage jewelry.
White Sapphire & Topaz
Real gemstones that look like diamond, but with less brilliance and a slightly 'sleepy' look. A thermal or multi-tester identifies them as not diamond.
Want to identify the whole piece, a gemstone, or a marking? Our free picture identifier identifies jewelry, gems, hallmarks, and anything else from one photo.
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Frequently Asked Questions
Sources & References
Our identification guides are researched from the authorities below and reviewed by the IdentifyThis team. AI photo identification is a helpful starting point — for anything involving safety (venomous species, edibility, or medical symptoms), always confirm with a qualified expert before acting.
- Gemological Institute of America — Gem & crystal identification
- FTC — Jewelry Guides: how gold, gems & pearls must be described
- Smithsonian — Insect & animal biology
Reviewed by the IdentifyThis team · Last updated August 2026