The short answer
Moissanite is the best balance for a gem-set watch worn often: harder than sapphire, with more fire than diamond, at a fraction of diamond’s price. Cubic zirconia gives a bright, clean white sparkle at the most modest price of the three, though it wears less well over years. Lab diamond is chemically identical to mined diamond and priced accordingly.
All three are made in a laboratory, and all three can set a bezel alight. What follows is how they differ — with the figures behind each claim, and a candid word on what we use.
The three stones at a glance
| Moissanite | Cubic zirconia | Lab diamond | |
|---|---|---|---|
| Material | Silicon carbide | Zirconium dioxide | Carbon |
| Hardness (Mohs) | 9.25 | 8–8.5 | 10 |
| Refractive index | 2.65–2.69 | 2.15–2.18 | 2.42 |
| Dispersion (fire) | 0.104 | ≈0.060 | 0.044 |
Hardness and everyday wear
The Mohs scale ranks scratch resistance from 1 (talc) to 10 (diamond). Lab diamond scores 10, moissanite 9.25 — harder than sapphire at 9 — and cubic zirconia between 8 and 8.5.
What matters on the wrist is the dust of ordinary life, which contains quartz at 7 on the scale. All three stones are harder than that, so none will scratch in normal wear. The difference shows over years rather than weeks: cubic zirconia can slowly gather micro-abrasions and lose a little of its edge, while moissanite stays crisp almost indefinitely.
Cubic zirconia is also a little more inclined to take a film from skin oils, which reads as cloudiness. It is not damage. Warm water, a drop of mild soap and a soft brush restore it in a minute.
Brilliance and fire
Two figures decide how a stone handles light. Refractive index measures how strongly it bends light back towards you — brilliance, the white flash. Dispersion measures how widely it splits light into color — fire, the rainbow flash.
Moissanite is higher than diamond on both, with more than twice diamond’s dispersion. Under direct light it throws visible rainbow sparks; most people love the effect, and a few find it livelier than diamond’s cooler white. Cubic zirconia sits closer to diamond in character, with a clean white light of somewhat lower intensity.
On a watch, one detail narrows the gap: pavé stones are small, often one to two millimeters across. At that size a well-cut cubic zirconia and a moissanite both read as a single field of light. The differences show most in larger stones — a bezel of bigger rounds, or a tennis bracelet worn beside the watch.
What each costs, and why
Cubic zirconia is grown quickly from inexpensive raw material by skull-crucible melting, a process in commercial use since the 1970s, so finished stones cost very little. Moissanite — first identified by the chemist Henri Moissan in 1893, in fragments from a meteor crater — is grown slowly as silicon carbide crystals, and its hardness makes it slower to cut. Lab diamond is grown by high-pressure or chemical-vapor processes and cut like mined diamond, and its price follows diamond’s.
For a watch set with hundreds of small stones, those differences compound. That is why a fully set moissanite watch is within reach, and a fully set diamond watch is not.
How to tell them apart
- Thermal testers measure how quickly a stone conducts heat. Moissanite conducts heat much as diamond does, so a thermal diamond tester reads it as diamond.
- Multi-testers also measure electrical conductivity, which separates moissanite from diamond reliably.
- Under a loupe, moissanite shows doubled facet edges when viewed at an angle — a property called birefringence — which neither diamond nor cubic zirconia shows.
- By weight, cubic zirconia is markedly denser: a CZ stone weighs about two-thirds more than a diamond of the same size.
Caring for each stone
All three stones are cared for in the same way, and none asks for much. Wipe the watch with a soft, dry cloth after wearing, so skin oils and lotion do not build up around the settings. Every few weeks, clean the stones with warm water, a drop of mild soap and a soft brush, then dry the watch thoroughly — keeping water away from the crown and case back, whatever the rating. Avoid ultrasonic cleaners on a watch: the vibration is unkind to the movement and to small settings.
Cubic zirconia benefits most from that routine, since it shows a film sooner. Moissanite and diamond, being harder, keep their polish with less attention. With any of the three, the setting matters more than the stone: store the watch apart from other jewelry, so harder stones cannot scratch softer metal, and have the settings checked if the watch takes a knock.
What we use, and why we say so
We set our watches with moissanite or cubic zirconia, and every listing names which. We do not describe either as diamond, and we do not need to: moissanite in particular is a gemstone in its own right, with properties diamond cannot match. Browse men’s watches or women’s watches, or read our guide to gem-set watch terms.