Is moissanite as brilliant as diamond for an engagement ring?

A 1.5 carat equivalent round moissanite has a refractive index of about 2.65 and a dispersion of 0.104. Diamond sits at 2.42 and 0.044. Those numbers explain most of what you need to know before asking whether moissanite is as brilliant as diamond for an engagement ring.

Moissanite's brilliance vs. diamond's

Brilliance and fire are different. Brilliance is white light coming back at your eye. Fire is the colored sparkle the stone throws off. Moissanite has more fire. Diamond has a more even balance between white light and fire. So no. Not in the way most people mean. Moissanite looks brighter in some lighting, more rainbow in others, and less crisp up close.

That last part matters. Moissanite is double refractive. Diamond is single refractive. Under a 10x loupe you can see doubled facet edges in moissanite, a slight fuzziness that a diamond doesn't have. To the naked eye it reads as less sharp. Some people never notice. Some people notice in a week and can't unsee it.

What happens in real life

Last fall a client named Priya came in with a photo of a 2 carat equivalent moissanite ring she'd seen online, and the photo made it look identical to a diamond, but in person under the store's LED spots the stone threw rainbows everywhere. She loved it for three days. Then she came back asking if we could swap the stone for something less disco. We couldn't just swap it. The moissanite was cut to slightly different angles than a diamond, sat lower in the head, and rebuilding it cost her $450 and two weeks.

That's the part most online photos hide. Moissanite throws more fire than diamond, especially in direct sun or under LED. Some clients want that. Some clients buy moissanite expecting a diamond look and end up annoyed every time the stone flashes blue and green at dinner.

Where moissanite wins

Cost is the obvious one. A premium 1.5 carat equivalent moissanite from Charles & Colvard runs somewhere around $400 to $600 loose. A lab-grown diamond of similar visual size with a good cut starts near $1,800 to $2,500. Natural is many times that. Moissanite is a 9.25 on the Mohs scale, so it won't scratch in daily wear. I set it in the same prongs and bezels I use for diamond.

Moissanite is sold by carat equivalent, not carat, because it's less dense than diamond. A 1 carat moissanite looks visually larger than a 1 carat diamond. That confuses people, and I don't blame them.

When I'd steer you away from it

If the goal is a ring that reads as a diamond, I'd take a well-cut 0.80 carat lab-grown diamond over a 2 carat moissanite, and that difference only gets more obvious as stone size goes up. Most moissanite over about 1.3 carats equivalent looks a little costume to me in direct sunlight. I say that knowing it loses me sales.

For small stones, under 0.75 carat equivalent, moissanite passes far more easily. The fire is less overwhelming at that scale, and the double refraction is harder to see. If you're stacking five tiny stones in a band, nobody will know. If you're fronting a 2.5 carat equivalent solitaire, people will ask, and not always in the way you want.

If you want the rainbow, buy the moissanite. If you want the stone to disappear into white light and look like a diamond, save for the diamond. I won't pretend they're interchangeable.