Moissanite vs cubic zirconia

On day one, in a store, a good cubic zirconia and a good moissanite can both look like a diamond to most people. The real difference shows up later. One of them still looks new after years of daily wear. The other scuffs, rounds off at the edges and starts to look foggy. That is the whole decision, and the numbers explain why.

The numbers side by side

Moissanite values are from GIA's Gems & Gemology study of the material. GIA's simulants overview puts CZ at 8.5 on the Mohs scale, dates it to the late 1970s and describes it as having a bit more fire but less brilliance than diamond; the CZ optical and density ranges are standard reference values.

Why hardness decides this

Ordinary household dust contains quartz, which sits at 7 on the Mohs scale. Anything softer than or close to quartz slowly gets abraded by daily life. Cubic zirconia at 8 to 8.5 resists that better than glass, but not completely. GIA notes that diamond simulants can develop scratches and visible abrasions with wear. On a CZ you see it first on the facet edges, which go from crisp to slightly rounded, and on the table, which picks up fine scratches. Scratched surfaces scatter light and hold grime, and together that reads as cloudy.

Moissanite at 9.25 is harder than sapphire and ruby. Dust cannot scratch it, so its facets stay sharp and its polish stays bright through years of wear. This is why moissanite is sold for engagement rings and CZ mostly is not.

Why moissanite looks brighter

Refractive index is how strongly a stone bends light; higher means more light comes back out of the top. Moissanite's 2.65 to 2.69 is above even diamond's 2.42. CZ's 2.15 to 2.18 is well below both, which is why a CZ often looks lively but a little soft or glassy next to the other two. Both simulants throw more colored fire than diamond. Moissanite throws the most, by a wide margin. If rainbow flashes bother you, neither is a perfect diamond look alike, and CZ is the milder of the two.

How to tell them apart

If you have a stone and do not know which it is, these checks split them quickly.

Weight

CZ is heavy. Its specific gravity is around 5.6 to 6.0, against 3.22 for moissanite, so a loose CZ weighs roughly 1.7 to 1.9 times as much as a moissanite of the same size. A loose stone that feels heavy for its size on a gem scale is CZ.

Tester

A basic thermal diamond tester reads moissanite as diamond and CZ as not diamond. A multi tester reads moissanite as moissanite and CZ as not diamond. Either way, a thermal pen alone separates these two. Details in how diamond testers work.

Loupe

With a 10x loupe, look through the side of the stone at an angle. Moissanite is doubly refractive and shows doubled back facet edges. CZ is singly refractive and does not double. On a worn CZ you will also see rounded edges and surface scratches.

Price and paperwork

Moissanite costs noticeably more and usually comes with a maker's certificate. A very cheap "diamond" with no paperwork is most often CZ. Our list of signs of a fake diamond covers the setting and stamp clues that go with it.

Which one for which piece

Settings say a lot

The metal around the stone usually tells you what the maker thought it was worth. CZ is most often set in sterling silver or plated base metal, because nobody pays for gold around a stone that costs very little. Moissanite is commonly set in solid gold or platinum, the same mountings used for diamonds. Check the inside of the band for a stamp: 10K, 14K, 18K, PLAT or 925.

That matters for value, too. When people try to sell a moissanite ring, the gold is often worth more than the stone. With CZ in silver, the whole piece is worth very little. Plan on that before you buy either one.

Which looks better after five years

That table is the practical meaning of the hardness numbers above. CZ costs less up front but tends to need replacing on a ring worn every day. Moissanite costs more once.

When CZ is the better choice

CZ wins in a few honest cases. If you want a big statement piece for one event, a stand-in ring for travel or the beach, or a fashion piece you will replace when the trend moves on, paying more for moissanite makes little sense. CZ also has less colored fire than moissanite, so some people find a fresh CZ reads as closer to diamond in bright sun. The tradeoff is time: that look holds for months of hard wear, not years. Buy CZ knowing it is temporary and it does its job well.

What neither stone is

• Neither is a diamond, and neither is a lab grown diamond. Both are simulants. If you want a lab made diamond, read are lab grown diamonds real.
• Neither has resale value. Buy for the look and the wear, not as an asset.
• Neither should be sold as diamond. The FTC Jewelry Guides treat that as deceptive.

Our take

Pay the extra for moissanite on anything you will wear daily for more than a year or two. The hardness gap is the difference between a stone that still looks new and one that looks tired. Save CZ for pieces you treat as disposable. If you are deciding between a simulant and a real diamond, compare against diamond vs cubic zirconia and diamond vs moissanite, and for the material itself see what is moissanite.

Worth being clear: everything here, and the app itself, is an educational reference. At-home tests narrow things down, they do not certify a stone. Before you buy, sell or insure anything of real value, get it looked at by a certified gemologist or an independent appraiser.