Lab-grown diamonds and cubic zirconia are both made in a lab and both look bright and colorless in a jewelry case, so they're easy to confuse. But they are completely different materials. One is a diamond; the other is an inexpensive diamond imitation. Here's how they differ in what they're made of, how they wear, how they sparkle and what they cost.
What is the difference between a lab-grown diamond and cubic zirconia?
A lab-grown diamond is a diamond: pure carbon with the same crystal structure, hardness and sparkle as a mined diamond. Cubic zirconia (CZ) is a different, man-made material, zirconium dioxide, designed to imitate a diamond. CZ is much softer, scratches and clouds over time, shows more rainbow color, and costs a tiny fraction of the price.
Lab-grown diamond vs cubic zirconia: side by side
| Lab-grown diamond | Cubic zirconia (CZ) | |
|---|---|---|
| What it is | A diamond, grown in a lab | A diamond simulant (imitation) |
| Composition | Pure carbon | Zirconium dioxide |
| Hardness (Mohs scale) | 10 | About 8 to 8.5 |
| Refractive index (brilliance) | 2.42 | About 2.15 to 2.18 |
| Fire (dispersion) | Balanced white and colored flashes | Stronger rainbow flashes that can look artificial |
| Weight for the same size | Lighter | Roughly 1.7 times heavier |
| Long-term wear | Stays bright and sharp-edged for life | Scratches, rounds at the edges and clouds over time |
| Diamond tester | Tests as diamond | Fails |
| Certification | Independently graded by IGI (full 4Cs) or GIA | Not graded by gem labs |
| Price | Far below a mined diamond | A small fraction of a lab-grown diamond |
Is a lab-grown diamond the same as cubic zirconia?
No. A lab-grown diamond is chemically, physically and optically the same as a mined diamond; only its origin differs. Cubic zirconia shares none of those properties. It's a separate crystal made to resemble a diamond at a glance. That's why jewelers call CZ a "simulant", while a lab-grown diamond is a diamond that must simply be described as lab-grown.
Which is more durable, a lab-grown diamond or CZ?
A lab-grown diamond, by a wide margin. Diamond is a 10 on the Mohs hardness scale, the hardest natural material, so everyday contact won't scratch it. Cubic zirconia is about 8 to 8.5. That's hard enough to look fine at first, but everyday dust contains quartz, which is a 7, and repeated knocks gradually scratch CZ, round off its facet edges and leave it looking hazy. For a piece worn daily, like an engagement ring, that difference shows within a few years.
Can you tell CZ from a diamond by looking at it?
Often, yes, especially side by side or after the CZ has been worn a while:
- Color of the sparkle. CZ throws stronger rainbow-colored flashes; a diamond shows a crisper mix of white brilliance and color.
- Surface wear. Worn CZ shows scratches and soft, rounded facet edges. A diamond's edges stay sharp.
- Clarity. CZ is usually flawless and very uniform, sometimes unnaturally so, and can have a faint gray or overly white look.
- Weight. A loose CZ feels noticeably heavier than a diamond of the same size.
- A diamond tester. A standard thermal tester reads a lab-grown diamond as diamond and CZ as not diamond. See do lab-grown diamonds pass a diamond tester?
Is cubic zirconia ever the better choice?
For some pieces, yes. CZ makes sense for costume and fashion jewelry, trend pieces you'll wear for a season, travel jewelry you don't want to worry about, or trying out a style before committing. For an engagement ring, a wedding band or anything you'll wear every day for years, a lab-grown diamond is the better choice. It keeps its look, can be independently certified, and costs far less than a mined diamond. If you want something in between, moissanite is a durable gemstone at a lower price than a lab-grown diamond.
Frequently asked questions
Is a lab-grown diamond a fake diamond?
No. A lab-grown diamond is a diamond, the same material as a mined diamond, grown in a controlled environment instead of underground. Cubic zirconia and other simulants are the imitations.
Will cubic zirconia pass a diamond tester?
No. CZ conducts heat very differently from diamond, so a standard thermal diamond tester reads it as not a diamond. A lab-grown diamond tests as diamond.
Does cubic zirconia get cloudy?
Over time, yes. CZ is much softer than diamond, so its surface gradually scratches and abrades, which leaves it looking cloudy even after cleaning. A diamond only looks cloudy when it's dirty.
Why is cubic zirconia so much cheaper?
CZ is inexpensive to manufacture in large quantities and isn't graded or certified like a diamond. A lab-grown diamond takes specialized equipment and time to grow, then must be cut, polished and independently graded.
Can a lab-grown diamond be certified?
Yes. IGI grades lab-grown diamonds on the same 4Cs scale as mined diamonds, and GIA places them in a "Premium" or "Standard" category. Every lab-grown diamond we sell is IGI or GIA certified. See IGI vs GIA.
Explore lab-grown diamonds
Learn how diamonds are graded in the 4Cs explained, compare lab-grown and natural diamonds, or browse certified Lab Diamond Rings and diamond stud earrings.
