Cubic Zirconia vs Lab Grown Diamond: quick comparison
This is the comparison that matters most to buyers looking for an affordable alternative to a mined diamond, because both options are laboratory-made and are frequently presented side by side as though they were variations on the same idea. They are not.
A laboratory-grown diamond is a diamond. Same carbon crystal, same hardness, graded on the same scales by the same laboratories, differing from a mined stone only in origin. Cubic zirconia is not a diamond. It is zirconium dioxide — a different material, developed specifically as a diamond simulant, and it behaves differently in the one way that matters most over time.
That shared fact of being made in a laboratory is what causes them to be confused. It is also almost the only thing they have in common.
| Property | Laboratory-grown diamond | Cubic zirconia |
| Is it a diamond? | Yes | No |
| Material | Crystalline carbon | Zirconium dioxide |
| Mohs hardness | 10 | About 8 to 8.5 |
| Clouds with daily wear | No | Yes, over time |
| Graded on the 4Cs | Yes, independent report | No |
| Dispersion (fire) | About 0.044 | About 0.058 to 0.066 |
| Density | About 3.52 | About 5.6 to 6.0 |
| Sold by | Carat weight | Millimetre size |
| Price level | Low relative to mined | Very low |
| Lifespan in daily wear | Permanent | Periodic replacement |
The short answer: for anything worn every day, the laboratory-grown diamond — it is an actual diamond, it will not cloud, and the price gap to cubic zirconia is far smaller than the gap to a mined stone. Cubic zirconia earns its place in occasional, costume and stand-in pieces, where permanence is not the point.
Appearance and design differences
A laboratory-grown diamond looks exactly like a mined diamond, because it is one. Cubic zirconia looks like a convincing imitation when new, and progressively less convincing as it wears.
The differences when both are new are real but subtle:
- Fire. Cubic zirconia has higher dispersion, so it throws more coloured flashes. In bright light it reads as livelier but slightly less crisp than a diamond.
- Brightness. Its refractive index is lower, so it returns less white light. A diamond reads brighter and cleaner.
- Weight and sizing. Cubic zirconia is roughly 1.7 times denser than diamond, so a stone of the same millimetre size weighs considerably more. Laboratory-grown diamonds are sold by carat weight like any diamond; cubic zirconia should be quoted in millimetres. If a simulant is quoted in carats, ask for the actual measurement.
- How they age. This is the difference that grows. A new cubic zirconia and a laboratory-grown diamond look far more alike than a three-year-old cubic zirconia and a laboratory-grown diamond. The simulant scratches, the facet edges soften and the surface loses its polish.
Neither material constrains the design. Both take any setting and any metal — though it is worth asking whether an expensive mount belongs around a stone that will need replacing.
Quality and technical differences: laboratory-grown disclosure, grading report, growth method where relevant and value trade-offs
Two completely different documents
This is the most practical difference between them. A laboratory-grown diamond comes with an independent grading report from a gemmological laboratory, recording cut, colour, clarity and carat on the scales in GIA’s grading methodology, stating laboratory-grown origin and any post-growth treatment. Report formats are described in GIA’s guide to report types, and you can verify the report number on the laboratory’s own database.
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 an honest arrangement for what it is — but it means the two cannot be compared on “quality” in any common language. One has verifiable grades; the other does not have grades at all.
How each is made
Laboratory-grown diamonds are produced by HPHT, which reproduces mantle-like pressure and temperature, or by CVD, which builds the crystal layer by layer from a carbon-rich gas. Cubic zirconia is produced by melting and crystallising zirconium dioxide with a stabiliser, at very large scale and very low cost. Both are manufactured, and that similarity tells you nothing whatever about the resulting material.
Identification is straightforward here
Unlike moissanite, cubic zirconia is easy for a jeweller to identify. It does not conduct heat the way diamond does, so a standard thermal diamond tester separates it immediately — and a laboratory-grown diamond will read as diamond on that same tester, correctly, because it is one. Density is also diagnostic, since a cubic zirconia of a given millimetre size is noticeably heavier. For any stone of value, the grading report remains the answer. See diamond certificate explained.
Price and value considerations
Cubic zirconia is cheaper than laboratory-grown diamond, but this is the comparison where the gap has narrowed most dramatically, and it is worth re-examining if you last looked a few years ago.
Laboratory-grown diamond prices have fallen substantially as production capacity expanded. For many specifications the difference between a laboratory-grown diamond and a good cubic zirconia is now modest relative to the cost of the setting — which means the practical question is no longer “can I afford a diamond?” but “how much am I actually saving by choosing a stone that is not one, and that will need replacing?”
Three further points:
- The setting dominates both quotes. With an inexpensive centre stone, metal and labour are the bulk of the cost. Either stone in a platinum halo is not a cheap ring.
- Replacement cost is real for cubic zirconia. A stone worn daily will need replacing periodically. Individually cheap; over decades, not nothing — and each replacement means the ring is off the hand.
- Neither has resale value. Laboratory-grown resale is limited; cubic zirconia has effectively none. Neither should be bought as an investment — jewellery is not a regulated investment product and we do not give financial advice.
For current laboratory-grown pricing structure see lab-grown diamond price South Africa.
Durability, maintenance or ownership trade-offs
This is where the two genuinely separate, and it should decide the question for anything worn regularly.
- Hardness. Laboratory-grown diamond is 10 on the Mohs scale; cubic zirconia is about 8 to 8.5. The scale is not linear, so the practical gap is very wide.
- Surface wear. A cubic zirconia worn daily accumulates fine scratches and gradually loses its polish, taking on a cloudy look. A laboratory-grown diamond does not — it is as hard as any diamond and will look the same in decades.
- Cleaning. Identical for both, but cleaning cannot restore a scratched simulant. That dullness is abrasion, not dirt.
- Chipping. Both can chip if struck at a vulnerable point; pointed and cornered shapes need protective settings either way.
- Maintenance model. A laboratory-grown diamond is a permanent component. A cubic zirconia in daily wear is a consumable one.
- Insurance and documentation. A laboratory-grown diamond can be documented and insured conventionally. Cubic zirconia is generally not worth insuring, though the mount may be.
Who each option suits
Laboratory-grown diamond suits you if
- The piece will be worn every day and should still look right in ten years.
- You want the ring to contain a diamond and to be able to say so accurately.
- You want an independently graded stone with a verifiable report.
- It is an engagement ring, where permanence and the recipient’s expectations both matter.
- You would rather buy once than replace a clouded stone every few years.
Cubic zirconia suits you if
- The piece is costume, fashion or occasional wear.
- You want a travel ring or a stand-in while something valuable stays at home.
- You are trying a design or a stone size before committing — a genuinely sensible use.
- You want maximum apparent size for a very small outlay and are comfortable saying what it is.
- You accept that the stone is a consumable rather than a permanent part of the piece.
Which option should you choose?
For anything worn daily, choose the laboratory-grown diamond. It is a real diamond, it is independently graded, it will not cloud, and the saving from choosing cubic zirconia instead is small relative to what you give up.
For occasional and costume pieces, cubic zirconia is the right tool and choosing it deliberately is sensible. Nobody needs a diamond in a piece worn twice a year.
The decision is really about permanence rather than price. Ask how often the piece will be worn and how long it is meant to last, and the answer usually presents itself.
Whichever you choose, insist that the material is stated explicitly in writing. The problem in this category is never the product — both are legitimate — it is a seller being vague about which one you are getting.
Continue to the relevant buying guide or book expert guidance
We can show a laboratory-grown diamond and a cubic zirconia of the same millimetre size together, with the price of each, so the decision is made from real figures rather than assumptions. Continue at lab-grown diamond rings South Africa, cubic zirconia vs diamond for the wider comparison, or the diamond buying guide.