Lab-Grown Diamonds vs Cubic Zirconia: The Real Difference
Lab-Grown Diamonds vs Cubic Zirconia: The Real Difference
At first glance a lab-grown diamond and a piece of cubic zirconia can look similar in a shop window, but they are fundamentally different materials. One is a real diamond; the other is a diamond simulant. Understanding the gap matters because it affects how your ring sparkles, how it wears over decades, and how much it is worth. This guide explains the science and the practical differences so you can shop with confidence.
In short: A lab-grown diamond is chemically and optically identical to a mined diamond and rates 10 on the Mohs hardness scale. Cubic zirconia (CZ) is a synthetic simulant made from zirconium dioxide, rates about 8–8.5, and tends to cloud and scratch over time. For an heirloom piece such as an engagement ring, a certified lab-grown diamond is the far better long-term choice.
What is a lab-grown diamond?
A lab-grown diamond is a genuine diamond, grown in a matter of weeks using High Pressure High Temperature (HPHT) or Chemical Vapour Deposition (CVD) technology that recreates the conditions under which natural diamonds form. It has the same carbon crystal structure, the same hardness, and the same fire and brilliance as a mined stone. Reputable stones are graded by independent laboratories such as IGI and GIA on the same 4Cs used for natural diamonds. You can read more in our beginner's guide to lab-grown diamonds and on our lab-grown diamonds hub.
What is cubic zirconia?
Cubic zirconia is a lab-made crystalline material composed of zirconium dioxide. It is a diamond simulant, meaning it is designed to imitate the look of a diamond without being one. CZ is inexpensive to produce, which is why it appears in costume and fashion jewellery. It contains no carbon and is not graded on the diamond 4Cs, because it is not a diamond at all.
The key differences
Hardness and durability. Diamond is the hardest known natural material at 10 on the Mohs scale. Cubic zirconia sits around 8–8.5, so it scratches more easily and the facet edges soften with daily wear. Everyday knocks that a diamond shrugs off will gradually dull a CZ.
Brilliance and fire. CZ actually has higher dispersion than diamond, giving it an intense, rainbow-heavy flash that can look artificial. A diamond's balance of white brilliance and coloured fire reads as more refined. Crucially, CZ tends to attract grease and cloud over, so it loses sparkle within a year or two unless cleaned constantly.
Colour and clarity over time. A quality lab-grown diamond stays bright and colourless for a lifetime. CZ can develop a slightly cloudy or yellowish cast as micro-scratches accumulate.
Value and certification. A lab-grown diamond is a real diamond with a gradable, certifiable value; cubic zirconia has negligible resale value. To compare how lab-grown stones sit against mined diamonds on price, see our natural vs lab-grown price comparison, and learn how grading works in our diamond education guides.
What about price in the UK?
A loose piece of cubic zirconia may cost only a few pounds, and CZ fashion rings often sell for under £50. A certified one-carat lab-grown diamond, by contrast, typically starts from around £600–£1,200 for the stone depending on cut, colour and clarity, with the finished ring priced according to the metal and setting. The premium buys you a stone that is genuinely a diamond, keeps its beauty for decades, and carries an independent certificate.
Which should you choose?
If you want a low-cost sparkle for a one-off outfit or a temporary travel piece, cubic zirconia does the job. For anything you intend to wear daily or keep for life – an engagement ring, a pair of diamond earrings, or an heirloom pendant – a certified lab-grown diamond offers real diamond hardness, lasting brilliance and genuine value, usually at a fraction of the price of an equivalent mined stone.
Frequently asked questions
Is a lab-grown diamond a real diamond? Yes. It has the same chemical composition, crystal structure and physical properties as a mined diamond, and is certified by the same laboratories.
Can a jeweller tell CZ and diamond apart? Easily. A trained gemmologist can distinguish them instantly using a thermal or electrical conductivity tester, magnification and weight, since CZ is much denser than diamond.
Does cubic zirconia pass a diamond tester? No. Standard testers measure how a stone conducts heat; CZ fails, whereas both natural and lab-grown diamonds pass.
