Crystals That Look Like Diamonds
Plenty of colourless stones sparkle like a diamond — but diamond is uniquely hard (Mohs 10), singly refractive and full of "fire". These are the crystals and gems most often mistaken for it, with the quick clues that give each one away. (No table-top test is foolproof — a jeweller's thermal probe is the only sure check.)
Diamond look-alikes at a glance
| Stone | Hardness | How to tell it from diamond |
|---|---|---|
| Clear Quartz | Mohs 7 | Much softer (Mohs 7 vs 10) with little fire; sometimes sold as "Herkimer diamond" but it's just quartz. |
| Zircon | Mohs 7.5 | Plenty of fire and high lustre, but doubly refractive — through a loupe the back facets look doubled; a diamond's never do. |
| Moissanite | Mohs 9.5 | The closest look-alike: nearly as hard (~9.25) and with even MORE fire than diamond, plus facet doubling — that extra rainbow gives it away, and it reads as moissanite on a tester. |
| Sapphire | Mohs 9.0 | Colourless sapphire (Mohs 9) is hard and bright but low in dispersion, so it lacks a diamond's fire. |
| Topaz | Mohs 8 | Colourless topaz (Mohs 8) was a classic simulant; less fire, and it has perfect basal cleavage. |
| Goshenite | Mohs 7.5–8.0 | Colourless beryl — vitreous, low dispersion and softer (~7.5–8); no real fire. |
| Danburite | Mohs 7–7.5 | Colourless and vitreous (Mohs 7–7.5) with far less brilliance and fire than diamond. |
| Phenakite | Mohs 7.5–8 | Rare colourless gem (Mohs 7.5–8); brighter than quartz but still well short of diamond's fire. |
See the photos
Frequently asked questions
What crystal looks most like a diamond?
Moissanite is the most convincing — it is nearly as hard as diamond and has even more fire. The giveaways are its extra rainbow flashes and doubled facet edges under a loupe, and it reads as moissanite on a thermal/electrical tester.
How can you tell a real diamond from a look-alike?
No single home test is conclusive, but diamond is the hardest material (Mohs 10), is singly refractive (facets never look doubled) and disperses light into bright "fire". Softer, doubly refractive or low-fire stones are simulants — confirm with a jeweller.