Lab-Grown vs Moissanite vs Cubic Zirconia —
Why They Are Not the Same

Someone, at some point, told you these were all basically the same thing. They were wrong. A lab-grown diamond, a moissanite, and a cubic zirconia are three different materials with different chemical compositions, different physical properties, and different long-term behaviours on your hand. Putting any of them in a ring does not make them interchangeable. Chemistry is not a matter of opinion.

If you have ever searched for a diamond online in India, you have almost certainly come across the phrase "American diamond." You may have wondered what it means. It means cubic zirconia. There is no such thing as an American diamond. We will get to that.

Moissanite — What It Is and What It Is Not

Moissanite was first discovered in 1893 by the French chemist Henri Moissan inside a meteor crater in Arizona. The natural material, silicon carbide, is extraordinarily rare on Earth. Nearly all moissanite sold in jewellery today is lab-created. That is worth knowing: moissanite is itself a lab-grown material. It is just not a diamond.

Silicon carbide and carbon are completely different compounds. Moissanite is harder than most gemstones at 9.25 on the Mohs scale, which makes it genuinely durable for daily wear. Its refractive index of 2.65 to 2.69 is higher than diamond's 2.42, which means it produces more fire, the coloured flashes of light you see when a stone catches light. Some people love this. Some people find it looks artificial compared to a diamond's more restrained, icier brilliance. Neither reaction is wrong.

Under magnification, moissanite shows double refraction — when you look through the stone, you see two of each facet edge rather than one. Diamond is singly refractive. A trained eye with a loupe can spot the difference. A gemological instrument confirms it in seconds.

Moissanite is priced lower than lab-grown diamonds for the same visual size. It is a legitimate choice if you understand what you are buying. The problem is when it is sold as "lab-grown diamond" without disclosure. This happens more often than it should, particularly in unbranded online listings. If a seller cannot produce an IGI certificate describing a stone as a diamond, you do not have a diamond.

Cubic Zirconia — What India Calls "American Diamond"

Cubic zirconia is zirconium dioxide. It contains no carbon. It has no structural relationship to diamond beyond a superficial visual similarity when new. It is the most widely used diamond simulant in the world, produced in industrial quantities for a cost measured in rupees per stone.

The hardness difference matters in practice. At Mohs 8 to 8.5, cubic zirconia can be scratched by quartz — one of the most common minerals in everyday dust and soil. Diamond at Mohs 10 cannot. A cubic zirconia ring worn daily will show surface scratches within months. By year two, the brilliance that made it look attractive when new will be significantly diminished. The stone clouds. It does not recover.

Cubic zirconia is also noticeably heavier than diamond for the same visual size. Diamond has a density of 3.5 grams per cubic centimetre. Cubic zirconia runs at 5.6 to 6.0. A stone that looks like a one carat diamond but sits lighter or heavier than expected is worth examining more closely.

How to Tell Them Apart Without a Lab

Ask for the certificate

A lab-grown diamond comes with an IGI certificate stating its 4C grades and the growth method. This certificate has a number you can verify at igi.org. Moissanite has its own grading reports from the Charles and Colvard or IGI but it will say moissanite, not diamond. Cubic zirconia has no grading certificate. If you ask for a certificate and none exists, you know what you are looking at.

Look at the fire

Hold the stone under a light and tilt it. Moissanite produces very obvious rainbow flashes, more than a diamond would at the same size. Cubic zirconia also produces strong fire when new but lacks the precise, crisp brilliance of a diamond. These are visual cues, not definitive tests. But they are a useful starting point.

Check the weight

Cubic zirconia is significantly heavier than diamond. If you have experience handling diamond jewellery, a CZ stone of the same apparent size will feel denser in your hand. This is a rough test only. For anything above a small purchase, ask for the certificate.

The heat test

Diamond conducts heat extremely well. A diamond tester measures this conductivity. Both lab-grown and mined diamonds pass. Moissanite also passes most basic diamond testers because its conductivity is similar, which is why newer testers have a moissanite-specific mode. Cubic zirconia fails all of them. A seller who will not allow testing has already told you something.

The Mislabelling Problem in India

Walk through any jewellery market or scroll through any major Indian e-commerce platform and you will find cubic zirconia sold as American diamond, moissanite sold as lab-grown diamond, and poorly plated alloy sold as gold. This is not a rare occurrence. It is the default.

The Indian consumer protection framework does not currently enforce gemstone disclosure with the same rigour as hallmarking rules for gold. Sellers understand this gap. Some exploit it deliberately.

Knowing the terminology is your first line of protection. If a listing does not specify the chemical composition of the stone, or uses vague phrases like "high-quality diamond" or "brilliant cut stone" without a certificate, the omission is intentional. A seller with a real diamond is not shy about saying so. They have a certificate that proves it.