What Is Moissanite? A Plain Guide for Diamond Shoppers

Moissanite is a crystal of silicon and carbon, called silicon carbide. Diamond is pure carbon. That one difference in chemistry gives the two stones different hardness, different sparkle and different test results, even when they look alike across a room.

The mineral was first identified in 1893 by the French chemist Henri Moissan in material from a meteorite crater in Arizona, and it is named after him. Natural moissanite is so rare that it plays no role in jewelry. Every moissanite you will see in a store was grown in a lab, a process that became commercial for gems in the late 1990s.

Moissanite is not a lab-grown diamond. A lab-grown diamond is carbon with diamond's crystal structure; moissanite is a different material entirely. Mixing them up is one of the most common mistakes in online jewelry listings. The difference is laid out in moissanite vs lab diamond.

Property	Moissanite	Diamond (natural or lab-grown)
Chemistry	Silicon carbide (SiC)	Carbon (C)
Mohs hardness	9.25	10
Refractive index	About 2.65 to 2.69	About 2.42
Dispersion (fire)	About 0.104	About 0.044
Optical character	Doubly refractive	Singly refractive
Thermal tester result	Often reads as diamond	Diamond
Electrical conductivity	Usually conducts	Usually does not
Can be called diamond	No	Yes (lab-grown must say lab-grown)

Dispersion is the number to notice. Moissanite splits light into colors more than twice as strongly as diamond, which is why it throws big rainbow flashes. Some people love that. Others find it reads as "not diamond" the moment it hits sunlight.

At 9.25, moissanite is harder than every common gem except diamond. It resists scratches well and holds a polish for years, which puts it far ahead of cubic zirconia (8 to 8.5) for daily wear. It does not get cloudy from the inside; if a moissanite looks hazy, the cause is usually soap film or skin oil on the surface, which cleaning removes.

Hardness is not toughness. Any gem can chip if it takes a hard hit on a thin edge or a point. Settings that protect corners and tips matter for moissanite just as for diamond.

Natural moissanite exists, but it is one of the rarer minerals on Earth. It turns up as tiny crystals in some meteorites and in a few rock formations, almost never larger than a grain. No natural moissanite large enough to cut into a jewelry stone is sold commercially.

Gem moissanite is grown in a lab by heating silicon and carbon sources until crystals form, then cutting and polishing them like any other gem. Because it is made in a factory, size and clarity are controlled, and stones are usually very clean. That is another small clue: a large, flawless, colorless "diamond" sold cheaply deserves a second look.

Moissanite's look differs from diamond in three ways a trained eye picks up:

• More rainbow. The higher dispersion means more colored flashes, especially in sunlight.
• Doubled facets. Look through the side of the stone with a 10x loupe and the back facet edges can appear doubled. Diamond shows single, crisp lines.
• Color. Early moissanite had a yellow or gray tint. Modern stones are sold as colorless or near-colorless, but some still show a faint tint in larger sizes.

Across a room, most people cannot tell moissanite from diamond. Up close, under a loupe or in direct sun, the differences show.

Stone	What it is	Mohs hardness	Sold as diamond?
Natural diamond	Mined carbon	10	Yes
Lab-grown diamond	Lab-grown carbon, same crystal as natural	10	Yes, disclosed as lab-grown
Moissanite	Lab-grown silicon carbide	9.25	No
White sapphire	Colorless corundum	9	No
Cubic zirconia	Lab-made zirconium dioxide	8 to 8.5	No
Glass	Silica glass	About 5.5	No

Among the stones that are not diamond, moissanite is the closest in hardness and the furthest in sparkle. That combination is what makes it popular, and what makes it the stone most often mislabeled.

Moissanite costs a fraction of a natural diamond, and usually less than a lab-grown diamond of the same size too. As lab-grown diamond prices fell after 2020, the price gap between moissanite and real diamond narrowed. In 2026 a shopper can buy a lab-grown diamond, which is real diamond, for a price that a few years ago only moissanite could match.

Real examples from our case, all diamond, all E color and VS1 clarity: the Round Lab Diamond Ring 1.5 ct, 14K White Gold is $2,000, and the Mixed Lab Diamond Ring 1.05 ct, 10K White Gold is $2,200. If the reason for choosing moissanite was price alone, compare those numbers before deciding. The full side-by-side is in moissanite vs diamond.

Moissanite is about 10% lighter than diamond for the same size, because it is less dense (roughly 3.2 grams per cubic centimeter against about 3.5 for diamond). A moissanite cut to the size of a 1 carat round diamond weighs less than a carat. To avoid confusion, many sellers describe moissanite by millimeters or by "diamond equivalent weight" (DEW), meaning the weight a diamond of the same size would have.

Round size	Diamond weight at that size (approx.)	How moissanite is usually listed
5.0 mm	About 0.5 ct	5 mm, or 0.5 ct DEW
6.5 mm	About 1 ct	6.5 mm, or 1 ct DEW
8.0 mm	About 2 ct	8 mm, or 2 ct DEW
9.3 mm	About 3 ct	9.3 mm, or 3 ct DEW

If a moissanite listing quotes plain carats with no DEW or millimeter size, ask which one it means. Diamond sizes in this table are typical for well-cut rounds; actual stones vary with cut proportions.

Basic diamond testers measure heat flow, and moissanite carries heat almost as well as diamond, so it passes. Jewelers catch it three ways:

1. Multi-tester. Adds an electrical test. Moissanite usually conducts; diamond usually does not.
2. Loupe. Doubled facet lines viewed through the side of the stone.
3. Lab report. A gem lab identifies it with certainty. GIA has documented moissanite stones carrying forged diamond inscriptions, caught through double refraction, dispersion and weight.

Step-by-step checks for any stone are in how to spot fake diamonds.

Moissanite is sold in colorless, near-colorless and fancy colors such as green, gray and blue. Some brands borrow diamond color letters to describe it, but there is no independent lab scale for moissanite the way GIA grades diamond, so treat those letters as the seller's own description and judge the stone by eye in daylight.

Moissanite is popular in iced-out chains, pendants and aftermarket watch bezels because it passes the cheap tester and costs less than diamond. That is fine when the piece is sold as moissanite. It becomes a problem when a listing says "VVS diamonds" or just "diamonds" and the stones are moissanite. "VVS" is a diamond clarity grade, and the FTC Jewelry Guides say a stone that is not diamond should not be described as one.

For iced watches, the questions go beyond the stones; see how to check diamonds on a watch and box, papers and serial numbers. If you are comparing moissanite with CZ in costume pieces, CZ vs moissanite explains the gap.

The FTC Jewelry Guides say a stone may only be called a diamond if it is one, and that lab-made gems must be described with words like "laboratory-created" or "lab-grown" next to the gem name. For moissanite, honest labels look like "lab-created moissanite" or simply "moissanite". Labels to be wary of: "moissanite diamond", "diamond simulant" without naming the stone, and "VVS ice" with no stone named at all.

Moissanite is cleaned the same way as diamond: warm water, a drop of mild dish soap and a soft toothbrush. It handles ultrasonic cleaners well when the setting is sound, and because it is so hard it rarely needs polishing.

If you want	Better fit
The lowest price for a large, hard stone	Moissanite
Maximum rainbow fire	Moissanite
A real diamond at a lower price	Lab-grown diamond
The classic white diamond sparkle	Diamond, natural or lab-grown
Rarity and resale value	Natural diamond

Whatever you choose, get the stone type written on the receipt. It costs the seller nothing, and it protects you. If you also wear gold daily, our note on why jewelry turns skin green covers the metal side.

Moissanite makes sense when you want a hard, bright, colorless-looking stone at the lowest price, you like strong rainbow fire, and you do not mind that the stone is not diamond. It is a common choice for travel rings, fashion pieces and first engagement rings on a tight budget.

It makes less sense when the word "diamond" matters to you or the person receiving it, when you plan to resell, or when you want the classic white diamond look in sunlight. Since lab-grown diamond prices fell, the price advantage has also shrunk: compare a moissanite quote against a lab-grown diamond of the same size before deciding. If you are shopping iced pieces, check every listing for the stone type in plain words, because "moissanite" and "diamond" are not interchangeable no matter how the piece looks in a photo.