No. Cubic zirconia is not a lab diamond, and it is not the same as a lab-grown diamond. They are two completely different materials that happen to share one thing: both are made by people rather than dug out of the ground.

That single shared fact is why the confusion exists, and it is a costly one to carry into a jewellery shop. Here is the difference in plain terms, and how to keep the two straight.

The one-sentence version

A lab-grown diamond is diamond — the same carbon crystal as a mined diamond, with the same hardness, the same sparkle and the same certificate. Cubic zirconia is a different substance entirely, made of zirconium oxide, that has been engineered to look a bit like diamond. One is the real material made a different way. The other is a lookalike.

What cubic zirconia actually is

Cubic zirconia — usually shortened to CZ — was developed in the 1970s, and it is a genuinely clever material. It is grown from zirconium oxide at very high temperature, and it is clear, colourless and cheap to produce at scale.

It is a diamond simulant. That is the correct trade word, and it means a stone that imitates the look of diamond without being diamond. Moissanite and white sapphire are also simulants, though they behave differently from CZ.

CZ has real uses. It is fine for costume jewellery, for a holiday piece you would not mind losing, or for a temporary stand-in. It is not sold dishonestly by reputable jewellers and there is nothing wrong with wanting it. The problem is only when it is presented as something it is not.

What a lab-grown diamond actually is

A lab-grown diamond is carbon, arranged in the diamond crystal structure, grown in a chamber that recreates the conditions diamond forms under. Chemically and physically it is diamond. It is graded on the same colour and clarity scales, by the same laboratories, and UK trading rules require it to be described as lab-grown so buyers know its origin.

It is not a simulant. It is not an imitation. It is the same material with a different history.

How they differ, side by side

	Lab-grown diamond	Cubic zirconia
What it is made of	Carbon	Zirconium oxide
Is it diamond?	Yes	No — a lookalike
Hardness	The hardest known natural material; 10 on the Mohs scale	Around 8 on the Mohs scale — scratches with wear
Weight for the same size	Normal for diamond	Noticeably heavier — around 1.6 times denser
Sparkle character	White brightness with flashes of colour	More rainbow flash, less white brightness
How it ages	Stays bright indefinitely with cleaning	Surface dulls and clouds over months and years of daily wear
Diamond tester result	Reads as diamond	Does not read as diamond
Certificate	IGI or equivalent grading report	Not graded or certificated
Cost	Considerably less than natural diamond, but a real purchase	Pennies by comparison

The difference you will actually notice: how it wears

If you take away one practical point, make it hardness. Diamond is the hardest material there is, which is why a diamond ring worn every day for thirty years still looks sharp. Cubic zirconia is much softer. It scratches against ordinary things — grit in a washing-up bowl, a stone worktop, the inside of a handbag.

Those scratches are individually invisible, but they accumulate on the facet surfaces, and scratched surfaces scatter light instead of reflecting it cleanly. That is why an old CZ looks cloudy and slightly grey while the metal around it still looks fine. It has not changed colour; its surface has simply been sandblasted by daily life.

A cleaning will not bring it back, because the damage is physical. This is the reason CZ is not used for engagement rings by anyone who expects the ring to be worn for decades.

Telling them apart

Unlike separating lab-grown from natural diamond — which needs a laboratory — separating CZ from diamond is straightforward.

• A thermal diamond tester distinguishes them immediately. Diamond conducts heat very well; CZ does not.
• Weight. A CZ of the same physical dimensions is noticeably heavier than a diamond. A jeweller can spot this on a scale in seconds.
• The look of the sparkle. CZ throws more rainbow colour and less crisp white light. Once you have seen the two next to each other it is hard to unsee.
• Edges under magnification. CZ facet junctions round off with wear; diamond edges stay sharp.

Why the two get confused

The mix-up is not the buyer’s fault. It comes from the word “lab”, which has been attached to both for different reasons.

Cubic zirconia has been made in laboratories since the 1970s, and for decades “lab-created stone” in a jewellery listing meant a simulant of some kind. Then genuine lab-grown diamonds arrived in volume, using very similar language for something completely different. If you learned the older meaning first, “lab” reads as “not real”, and the newer product gets tarred with it.

Some online listings make it worse. Phrases like “lab created diamond simulant”, “lab diamond CZ” or “diamond-quality zirconia” jam the two vocabularies together, sometimes carelessly and sometimes deliberately. The word that decides it is simulant. If it appears anywhere in the description, the stone is not diamond, no matter what else the listing says.

The words to look for on a listing

• Means it is diamond: lab-grown diamond, laboratory-grown diamond, lab-created diamond, man-made diamond, cultured diamond.
• Means it is not diamond: cubic zirconia, CZ, diamond simulant, diamond substitute, diamond-look, diamond-style, faux diamond, moissanite.
• Tells you nothing on its own: “brilliant”, “sparkling”, “AAAAA grade”, “VVS quality” used without a laboratory report. None of these are graded terms when applied to a simulant.

The reliable test is paperwork. A lab-grown diamond of any real size comes with a grading report from an independent laboratory such as IGI, and usually a matching laser inscription on the girdle of the stone. Cubic zirconia has neither, because there is nothing to grade and no value to protect.

Which should you buy?

If the piece is meant to last — an engagement ring, a wedding band, an anniversary gift — buy diamond. Lab-grown makes that far more affordable than it used to be, which is precisely why the CZ argument has weakened in recent years. If the piece is fashion jewellery you will wear for a season, CZ is a perfectly sensible choice and nobody should make you feel otherwise.

What you should never do is buy something described vaguely. “Diamond simulant”, “diamond look”, “diamond-style” and “CZ” all mean not diamond. “Lab-grown diamond”, “laboratory-created diamond” and “man-made diamond” all mean diamond. Sellers are required to be clear; if one is not, that tells you enough.

What we sell

We use lab-grown diamonds only. We do not sell cubic zirconia, and we do not set simulants in any piece. Every centre stone carries a free IGI certificate stating what it is.

If you have been looking at CZ rings and want to see what the diamond equivalent costs, the minimalist round cut engagement ring is our most affordable engagement design at £587, correct at the time of writing. The solitaire round cut engagement ring is the classic version at £657, and the stackable rose cut wedding band in sterling silver starts at £489 if you want diamonds in a band rather than a solitaire.

All prices correct at the time of writing. Everything is hand-made in solid gold or platinum, with free insured UK delivery and 30 days to return. Browse the engagement ring collection or the women’s jewellery collection.

Common questions

Is cubic zirconia a lab diamond?

No. Both are made in laboratories, but CZ is zirconium oxide and a lab-grown diamond is carbon. Only one of them is diamond.

Will cubic zirconia pass a diamond tester?

No. A standard thermal tester distinguishes CZ from diamond straight away. A lab-grown diamond does pass, because it is diamond.

Does cubic zirconia go cloudy?

With daily wear, yes. The surface accumulates fine scratches that scatter light. Cleaning helps briefly but cannot reverse it, because the damage is to the surface itself.

Is cubic zirconia worth anything?

Very little. It is inexpensive to produce and there is no resale market. Buy it for how it looks now, not as something to keep.

Is moissanite the same as cubic zirconia?

No, they are different again. Moissanite is silicon carbide, much harder than CZ and more durable, with a distinctive rainbow flash. It is still not diamond, but it wears far better than cubic zirconia. We compare the two properly in our guide to whether a lab-grown diamond is a moissanite.

Is zirconium the same as cubic zirconia?

No, and this one catches people out constantly. Zirconium is a grey metal used for wedding bands. Cubic zirconia is a clear stone. They share part of a name and nothing else — we explain the metal separately in our guide to zirconium wedding rings.

If you are weighing up a budget and want to know what is realistically achievable in real diamond, tell us the figure and we will show you honestly what it buys.