Diamond Basics
Cubic Zirconia vs Diamond: What Is the Difference?
Cubic zirconia looks like a diamond at first glance, but it is a very different stone. We explain the differences in hardness, light, weight and durability, and the first clues you can check at home.
3 min readUpdated: October 7, 2026
Short answer: Cubic zirconia looks like diamond but is not diamond. Diamond is pure carbon with a Mohs hardness of 10; cubic zirconia is zirconium oxide with a hardness of about 8–8.5. Cubic zirconia gives more coloured fire, bends light less than diamond, is about 1.7 times heavier, and scratches and goes cloudy over time. A diamond keeps the light of its first day even after many years.
What is “zircon”? Two different stones
In everyday Turkish, “zirkon” usually means cubic zirconia: a material made in a laboratory and used to imitate diamond. In nature there is also a separate mineral called “zircon”, which is another stone again. Neither is a diamond. In this article we cover cubic zirconia, the one most often found in jewellery.
Cubic zirconia and diamond compared
| Property | Diamond | Cubic zirconia |
|---|---|---|
| Composition | Pure carbon | Zirconium oxide |
| Hardness (Mohs) | 10 | About 8–8.5 |
| Refractive index | 2.42 | About 2.15–2.18 |
| Coloured fire | Balanced | More, “rainbow-like” |
| Density | 3.52 g/cm³ | About 5.6–6 g/cm³ |
| Thermal conductivity | Very high | Low |
| Over time | Keeps its light | Scratches, goes cloudy |
Clues you can see
- Fire: Cubic zirconia gives more coloured flashes than diamond in light; the “rainbow” effect is especially clear under spotlights. In diamond, white light and coloured fire are more balanced.
- Perfection: Because it is manufactured, cubic zirconia usually has no marks at all and is completely colourless. A flawless, very large but very cheap “diamond” should raise suspicion.
- Wear: On cubic zirconia that has been worn for a while, small scratches and wear show on the edges, and the surface goes dull.
- Weight: At the same size, cubic zirconia is noticeably heavier than diamond; with loose stones, a precise scale shows this.
These clues give a hint but are not conclusive. The way to tell for certain is an instrument and a report.
Telling them apart for certain: tester and report
Diamond conducts heat very well; cubic zirconia does not. Jewellers’ diamond testers measure this difference and identify cubic zirconia within seconds. An independent laboratory report documents both that the stone is a diamond and its origin. How does a diamond tester work? · How to tell if a diamond is real.
A lab-grown diamond is not cubic zirconia: a lab-grown diamond is also made in a laboratory, but it is not an imitation like cubic zirconia; it is a real diamond with the same chemistry, hardness and light as a natural diamond. It tests as diamond on a tester too. What is a lab-grown diamond?
Why diamond?
Cubic zirconia may suit a short-lived fashion piece; but for a solitaire or wedding band that will be worn every day and should keep its light for years, a diamond’s hardness and light are in another league. A lab-grown diamond offers that difference on a more affordable budget. Should you buy a lab-grown diamond?
Frequently asked questions
No. Cubic zirconia is a stone that looks like diamond but is made of a different material (zirconium oxide). It is softer and bends light differently. The stone itself does not darken, but its surface scratches and goes dull, and over time it looks cloudy. A diamond keeps its light because it does not scratch. Home tests are not conclusive. Extra coloured fire and wear on the edges can be clues; for a certain answer you need a jeweller’s tester or a laboratory report. No. Because cubic zirconia does not conduct heat well, it does not show as diamond on a diamond tester.Is cubic zirconia a diamond?
Does cubic zirconia darken over time?
How do you tell cubic zirconia from diamond at home?
Does cubic zirconia test as diamond?
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