Cubic Zirconia vs Diamond: quick comparison
These are two different materials, and everything else follows from that. A diamond is crystalline carbon. Cubic zirconia is zirconium dioxide — a laboratory-made crystal developed as an inexpensive diamond simulant, and produced in very large quantities.
Cubic zirconia is not a diamond and is not graded on the diamond scales. It is a legitimate product sold openly as what it is, and for plenty of purposes it is exactly the right choice. It only becomes a problem when it is described as a diamond, or when a buyer is not told which they are getting.
The honest headline difference is durability. Cubic zirconia is considerably softer than diamond, and a stone worn every day will gradually scratch and cloud in a way a diamond never will. That single fact should drive the decision more than price does.
| Property | Diamond | Cubic zirconia |
| Material | Crystalline carbon | Zirconium dioxide |
| Mohs hardness | 10 | About 8 to 8.5 |
| Refractive index | About 2.42 | About 2.15 to 2.18 |
| Dispersion (fire) | About 0.044 | About 0.058 to 0.066 |
| Density | About 3.52 | About 5.6 to 6.0 |
| Graded on the 4Cs | Yes | No |
| Clouds with daily wear | No | Yes, over time |
| Price level | High | Very low |
| Resale market | Established for mined stones | None |
The short answer: if the piece is worn every day and is meant to last, buy a diamond — and if budget is the obstacle, look at a laboratory-grown diamond before you look at a simulant. If the piece is occasional, temporary, a travel stand-in or a costume item, cubic zirconia does the job at a fraction of the cost and there is no reason to avoid it.
Appearance and design differences
When new and well cut, a good cubic zirconia looks convincingly like a diamond to most people. That is what it was developed to do. The differences are real but subtle, and they become more apparent with size and with time.
Fire. Cubic zirconia has higher dispersion than diamond, so it throws more coloured flashes. In bright light this reads as slightly excessive rainbow sparkle — livelier than a diamond, and to a trained eye obviously so.
Brightness. Its refractive index is lower than diamond’s, so it returns less white light. The result is a stone that flashes colour more but reads slightly less bright and less crisp.
Weight. Cubic zirconia is far denser than diamond — roughly 1.7 times. A cubic zirconia of the same millimetre size weighs considerably more, which is why it should be quoted in millimetres rather than carats. If a simulant is quoted in carats, ask for the actual measurement.
And the difference that grows. A new cubic zirconia and a diamond look far more alike than a three-year-old cubic zirconia and a diamond. Scratching dulls the facet edges and the surface, and the stone loses the crispness it started with. This is the difference nobody notices at purchase and everybody notices later.
On design, cubic zirconia imposes no constraints on setting style — but it is worth thinking about whether an expensive mount is the right home for a stone that will need replacing.
Quality and technical differences: 4Cs, certification, design suitability, price factors and the buyer’s next decision
Simulant is a precise term
A simulant is any material that resembles a diamond without being one — cubic zirconia and moissanite are both simulants. This is a different category from a laboratory-grown diamond, which is diamond: same carbon crystal, same hardness, graded on the same scales. Conflating the two is the commonest confusion in this subject, and it matters because the three products behave completely differently. See lab-grown vs natural diamond.
Grading works differently
Diamonds are graded on cut, colour, clarity and carat using the scales in GIA’s grading methodology, and issued independent reports as described in GIA’s guide to report types. Cubic zirconia is not graded on those scales and receives no independent gemmological report. It is sold by size and by a manufacturer’s quality description. That is not a deficiency — it is a different product — but it does mean you cannot compare a cubic zirconia’s “quality” against a diamond’s grades.
Telling them apart
Unlike moissanite, cubic zirconia is straightforward for a jeweller to identify. It does not conduct heat the way diamond does, so a standard thermal diamond tester distinguishes it immediately. Its much higher density is also diagnostic: a cubic zirconia of a given millimetre size is noticeably heavier than a diamond of the same dimensions. For a stone of any value, though, an independent report remains the answer — see diamond certificate explained.
Price and value considerations
Cubic zirconia costs a very small fraction of what a diamond of equivalent size costs. That gap is its entire purpose and it is not in dispute.
What is worth thinking about is the total cost of the piece rather than the stone. Three points follow.
The setting becomes the whole cost. With an effectively free centre stone, the metal and labour are the quote. A cubic zirconia in a platinum mount is not a cheap ring — and it puts a permanent, expensive setting around a stone that will need replacing.
There is no resale value at all. Cubic zirconia should be treated as having none. Neither material should be bought as an investment — jewellery is not a regulated investment product and we do not give financial advice — but the difference here is absolute rather than a matter of degree.
Compare against laboratory-grown before deciding. If cost is the only reason cubic zirconia is on your list, price a laboratory-grown diamond at the same millimetre size first. It is an actual diamond with an actual grading report, it will not cloud, and the gap is smaller than most people assume.
Durability, maintenance or ownership trade-offs
This is where the two materials genuinely diverge, and it is the section that should decide the question.
- Hardness. Diamond is 10 on the Mohs scale. Cubic zirconia is roughly 8 to 8.5. That sounds close, but the Mohs scale is not linear — the practical gap is very wide, and it is the single most important difference between the two materials.
- Surface wear. This is the consequence that matters. A cubic zirconia worn daily will accumulate fine scratches on its facets and table over months and years, and as those build up the stone loses its polish and takes on a cloudy, slightly greyish look. A diamond does not do this.
- Cleaning. Both clean the same way, but cleaning will not restore a scratched cubic zirconia — the dullness is abrasion, not dirt.
- Chipping. Both can chip if struck at a vulnerable point. Pointed and cornered shapes need protective settings in either material.
- Replacement rather than repair. The realistic maintenance model for a cubic zirconia in daily wear is periodic replacement of the stone, which is inexpensive. A diamond is a permanent component.
- Insurance. A diamond of any size should be documented and insured. Cubic zirconia is not worth insuring separately, though the setting may be.
Put plainly: a diamond bought today will look the same in thirty years. A cubic zirconia worn daily will not look the same in three. Neither fact is a criticism — they are simply different products for different jobs.
Who each option suits
Cubic zirconia suits you if
- The piece is occasional, costume or fashion jewellery rather than something worn daily.
- You want a travel ring or a stand-in while a valuable piece stays at home.
- You are testing a design or a size before committing to a diamond — a genuinely sensible use.
- You want maximum apparent size for a very small outlay and are entirely comfortable saying what it is.
- You accept that the stone will need replacing periodically if worn often.
A diamond suits you if
- The piece will be worn every day and is meant to last.
- The stone being a diamond matters to you or to the person wearing it.
- You want an independently graded stone with a report you can verify.
- You want something that can be passed on.
- You would rather buy once than replace a clouded stone every few years.
Which option should you choose?
For an engagement ring or any piece intended to be worn permanently, buy a diamond. The durability difference is not marginal, and a stone that goes cloudy in a ring meant to last is a disappointment that arrives slowly and cannot be fixed.
If budget is the obstacle, the answer is a smaller diamond or a laboratory-grown one — not a simulant. A modest, well-cut diamond in a simple setting will still be crisp in twenty years. A large cubic zirconia will not.
For occasional wear, travel, costume pieces or trying a design before committing, cubic zirconia is genuinely useful and inexpensive, and choosing it deliberately is sensible rather than second-best.
One rule either way: whatever you buy, get the material stated in writing. A seller who is vague about whether a stone is diamond, laboratory-grown diamond or cubic zirconia is the problem, whichever it turns out to be.
Continue to the relevant buying guide or book expert guidance
If cost brought you to this page, let us price a laboratory-grown diamond at the size you have in mind before you decide — it is an actual diamond and the gap is usually smaller than expected. Continue at diamond buying guide, lab-grown vs natural diamond or moissanite vs diamond for the other common simulant.
Compare a diamond against the alternatives