Cubic zirconia, diamond or moissanite: how to tell them apart

Cubic zirconia (CZ), diamond and moissanite are three different materials that can all look like a clear, bright stone. Diamond is natural carbon and the hardest of the three; moissanite is a lab-made silicon carbide that sparkles with more rainbow colour; cubic zirconia is a lab-made zirconium oxide that is softer and far cheaper. A careful look gives clues, but only a jeweller with a proper tester can confirm a diamond.

In Pakistan, CZ is often sold as “American diamond” or “AD”, and sometimes loosely as “zircon”, which is actually a different natural mineral. None of those names means diamond.

The three stones compared

Hardness, and why it matters on a ring

Rings take more knocks than any other jewellery. Diamond at 10 on the Mohs scale resists nearly everything. Moissanite is close behind. Cubic zirconia at around 8 to 8.5 is still harder than most things it meets, but everyday dust contains quartz at 7, and over years that is enough to wear the sharp facet edges and leave a CZ looking slightly soft or cloudy.

This is not a reason to avoid CZ. It is a reason to clean it gently and treat it as a stone with a lifespan of years of good looks, rather than generations.

Sparkle: brilliance versus fire

Sparkle has two parts. Brilliance is the white light a stone returns; fire is the flashes of rainbow colour. Diamond has strong brilliance and moderate fire. Moissanite has even more brilliance and much stronger fire, which is its biggest giveaway — in sunlight it throws obvious rainbows. CZ has plenty of fire but less brilliance, so it can look slightly glassier next to a diamond.

Simple checks you can do

None of these proves a diamond on its own. Together they tell you whether a stone is worth taking to a jeweller.

1. 1The fog test: breathe on the stone. On a diamond, which disperses heat quickly, the fog clears almost instantly. On CZ, it lingers for a couple of seconds. Clean the stone first, as grease affects the result.
2. 2Look for rainbow flashes in sunlight. Very strong, colourful flashes suggest moissanite or CZ rather than diamond.
3. 3Check the price. A ring sold as diamond at a fashion jewellery price is not a diamond.
4. 4Look at the metal stamp. Real diamonds are rarely set in unmarked base metal.
5. 5Look at the edges with a magnifier. Worn, rounded facet edges on an older stone point to CZ.
6. 6Ask a jeweller to test it. A standard thermal diamond tester separates diamond from CZ, but moissanite can pass a basic thermal test; a combined tester that also checks electrical conductivity is needed to tell diamond from moissanite.

Carats and millimetres

Carat is a measure of weight, not size. Because CZ is much denser than diamond, a CZ stone the same size as a one-carat diamond weighs considerably more. For that reason CZ is best described in millimetres. A round diamond of about 6.5 mm is roughly one carat; a CZ of 6.5 mm looks the same size but a “one carat” label on it means very little.

What an honest listing looks like

The problem is not CZ. CZ is a perfectly good stone that makes beautiful jewellery affordable. The problem is listings that blur the line between materials. When buying online, check that the listing does the following.

• Names the stone plainly: cubic zirconia, moissanite, lab-grown diamond or natural diamond.
• Does not use “diamond” alone for anything that is not a diamond, including phrases such as “diamond cut” or “diamond look” without explanation.
• States the metal and whether it is plated.
• Gives the stone size in millimetres for CZ, and carat weight plus a certificate for real diamonds.
• Is backed by a clear exchange policy and a contact who answers questions.

More on judging sellers is in our guide to spotting a fake online jewellery seller, and if you are choosing a ring for a mangni, see our overview of engagement ring designs.

Keeping a CZ ring bright

Most dullness on a CZ is not wear at all but a film of soap, lotion and skin oil on the back of the stone, which blocks light from entering. Soak the ring for a few minutes in lukewarm water with a drop of mild washing-up liquid, brush behind the stone with a soft baby toothbrush, rinse and pat dry. Take it off for housework and store it separately so harder stones cannot scratch it.

Which should you choose?

• Diamond: for a ring meant to last generations, carry value and be worn for decades.
• Moissanite: for near-diamond durability with more rainbow sparkle at a lower price.
• Cubic zirconia: for fashion rings, occasion rings, trying a style, or everyday sparkle without worry about loss.

Zayr's women's rings are set with cubic zirconia in clear and coloured stones, over rhodium- or gold-plated hypoallergenic bases. We do not sell diamonds or moissanite, and we will never describe a CZ as either.

A cubic zirconia ring is an honest purchase. It only becomes a bad one when somebody calls it a diamond.