Lab-Grown Diamond vs Moissanite vs Cubic Zirconia: What Each Stone Is and How to Tell Them Apart

Updated October 30, 2026

The short answer: Only one of the three is a diamond. A laboratory-grown diamond is crystallized carbon with the same chemical, physical and optical properties as a mined diamond; it's simply made in a factory instead of found in the ground. Moissanite (silicon carbide) and cubic zirconia (CZ, zirconium oxide) are different materials. GIA and IGI both call them diamond simulants: stones that look like diamond but don't share its properties. On the Mohs scale, diamond is 10, synthetic moissanite 9.25 and CZ 8.5, according to GIA. Moissanite shows more than twice the fire of diamond and is doubly refractive, so its back facets can look doubled; CZ has slightly more fire but less brilliance than diamond, and GIA notes colorless CZ may yellow over time. A laboratory-grown diamond can only be called a "diamond" under the FTC's Jewelry Guides, and only with a clear "laboratory-grown" (or similar) qualifier. Moissanite and CZ can't be called diamonds at all.

We sell loose laboratory-grown diamonds only, each with an IGI or GIA grading report. We don't sell moissanite or cubic zirconia. Everything below about properties and appearance comes from GIA and IGI, and the labeling rules come from the FTC's Jewelry Guides (16 CFR Part 23); sources are listed at the end.

Lab-grown diamond vs moissanite vs CZ at a glance

Laboratory-grown diamond Synthetic moissanite Cubic zirconia (CZ)
What it is Diamond: carbon crystallized in the cubic (isometric) system Silicon carbide, a different material Zirconium oxide, a different material
Classified as Diamond (FTC 16 CFR 23.12, with a "laboratory-grown" qualifier) Diamond simulant (GIA, IGI) Diamond simulant (GIA, IGI)
Mohs hardness 10 (FTC definition; IGI) 9.25 (GIA) 8.5 (GIA)
Refractive index 2.42 (FTC definition) 2.648 and 2.691, doubly refractive (GIA, Gems & Gemology) Not listed by GIA's guides; GIA says less brilliance than diamond
Fire Same dispersion as mined diamond (IGI) More than twice diamond's fire (GIA) Slightly more fire than diamond (GIA)
Look under magnification No doubled facets Doubled back facets; inside may look blurry (GIA) Usually colorless and very clean (GIA)
Color over time Graded on the D-to-Z scale like mined diamond Colorless to near colorless; some look slightly yellow or gray at certain angles (GIA) GIA: colorless CZ "may yellow over time"

What a laboratory-grown diamond is

The FTC defines a diamond as "a mineral consisting essentially of pure carbon crystallized in the isometric system," with a hardness of 10, a specific gravity of about 3.52 and a refractive index of 2.42. A laboratory-grown diamond meets that definition. It's grown by one of two methods, HPHT or CVD (see our guide to CVD vs HPHT lab-grown diamonds), then cut and polished like any diamond.

GIA puts it plainly: "Lab-grown diamonds have the same chemical, physical and optical properties as natural diamonds, while simulants do not." IGI says the same from the lab's side: lab-grown diamonds "are not imitation gems like cubic zirconia or Moissanite, which are 'simulants' that simulate diamond properties. They are real diamonds." IGI adds that lab-grown diamonds have "the same refractive index and optical qualities as natural diamonds" and are graded on the same color and clarity scales.

The practical result: everything you know about choosing a diamond applies. Cut, color, clarity and carat work the same way; our 4Cs guide for lab-grown diamonds covers them. What separates a laboratory-grown diamond from a mined one is origin, not appearance, and that takes laboratory testing. Our guide to laboratory-grown vs natural diamonds explains the differences that do exist.

What moissanite is

Moissanite is silicon carbide. GIA says colorless synthetic moissanite became popular as a diamond imitation in the late 1990s and "has become a very popular engagement ring stone due to its brilliance, intense fire and durability." Here's what GIA reports about it:

  • Hardness. 9.25 on the Mohs scale. GIA calls it "the hardest of all the diamond simulants," and very durable, "although not as hard as diamond."
  • Fire and brilliance. GIA says moissanite "has more than twice the fire of diamond and slightly more brilliance." In sizes of one carat or above, GIA notes, that intense fire "may give it away as a non-diamond gem," and in very large sizes the effect is sometimes called the "disco ball" effect.
  • Double refraction. Moissanite is doubly refractive, so "viewers will see a double image of its back facets," and the inside "may appear blurry." GIA's journal notes that this doubling of facet junctions is how moissanite is readily separated from diamond.
  • Color. GIA says moissanite can be colorless to near colorless, and some "look slightly yellow or gray when viewed at certain angles." It is also made in colors such as yellow, black and blue.
  • Clarity. GIA says moissanite "tends to have a few more inclusions than CZ," with minor, if any, imperfections.

GIA's journal Gems & Gemology published the original technical study when moissanite reached the jewelry market. It gave synthetic moissanite refractive indices of 2.648 and 2.691, a dispersion of 0.104, a Mohs hardness of 9¼ and a specific gravity of 3.22, and concluded it was "much closer to diamond in overall appearance and heft than any previous diamond imitation." The same study found that thermal probes of the day reacted to moissanite as if it were diamond, a problem that still matters (more on that below).

What cubic zirconia is

Cubic zirconia is zirconium oxide. GIA says it was introduced in the late 1970s and "has surpassed" every earlier diamond imitation in popularity. It's made by heating powdered zirconium oxide to its melting point and letting crystals grow as the melt cools. From GIA:

  • Hardness. 8.5 on the Mohs scale, "a hard and durable gem although not as hard as diamond." GIA's simulant guide adds that CZ "scratches more easily than diamond."
  • Fire and brilliance. CZ "has slightly more fire but less brilliance than diamond." GIA notes that some people find its "broad flashes of color" look artificial.
  • Clarity and color. Most CZ is colorless and has "high clarity with minute, if any, imperfections." But GIA also states that "CZ will, however, yellow in color over time."
  • Colors. CZ can be made in almost any color, and GIA says pink and yellow CZ can be convincing imitations of pink or yellow diamonds. If you're shopping for color, our guide to how fancy color lab-grown diamonds are made, graded and disclosed explains what a colored diamond's report shows.

How the three differ in everyday wear

Scratches and wear. Hardness is resistance to scratching. GIA explains that diamond, at 10, "is harder than any simulant," which means "most diamonds will hold up to daily wear and tear, while many simulants might soon develop scratches and visible abrasions, especially along facet junctions." Moissanite at 9.25 is close; CZ at 8.5 is further behind. GIA also notes that diamond's hardness lets it take a better polish, so diamonds have "a brighter luster than most simulants." Whatever the stone, the setting protects it; our guide to buying a loose lab-grown diamond for a custom setting covers what to discuss with your jeweler.

Sparkle. This is where taste comes in. Diamond's look is the reference point. Moissanite throws noticeably more colored fire, which some people love and others feel looks "different." CZ shows broad flashes of color with less brilliance. GIA's advice on simulants is to see the stone in person "to see if its unique sparkle and fire suit your taste." For a diamond bought online, the 360° video is the closest substitute.

Size for the weight. GIA notes that simulants have different densities from diamond, so a simulant can look larger or smaller than a diamond of the same carat weight. The Gems & Gemology figures put moissanite's specific gravity (3.22) a little below diamond's (about 3.52 under the FTC definition), so carat weights between the two materials don't translate one-to-one. For diamonds, compare millimeters on the report; our lab-grown diamond size chart shows real face-up sizes by shape.

Care. GIA lists both CZ and synthetic moissanite as safe for ultrasonic and steam cleaning, and says all simulants can be cleaned with warm soapy water. GIA also notes moissanite "is less likely to attract grease than diamond."

Why a handheld tester can get it wrong

Many jewelers use quick handheld testers. IGI warns that they have real limits with these three stones:

  • Moissanite can test as diamond. IGI says thermal testers "frequently give 'false-positives' when it comes to moissanite," because diamond and moissanite handle heat similarly. GIA's Gems & Gemology study found the same when moissanite first appeared: thermal probes reacted to it "as if it were 'diamond.'"
  • Lab-grown diamonds can test as moissanite. IGI says electrical testers "can mistake certain lab grown diamonds for moissanite." The HPHT growth process uses a metal catalyst, and its remnants can make a stone conductive. Blue diamonds containing boron can also conduct.
  • No tester separates lab-grown from mined. IGI says handheld testers are commonly used to tell diamond from simulants like CZ and moissanite, but thermal testers "make no distinction between lab grown diamond and natural diamonds."

IGI's conclusion is that separating these stones reliably is a job for a gemological laboratory, and that diamonds and other gemstones should come with a grading report "whenever they change hands." That's the practical point of this whole comparison: you can't confirm what a stone is by eye or with a pocket tester, but you can by checking its report.

What the FTC requires sellers to call each stone

The FTC's Jewelry Guides cover "gemstones and their laboratory-created and imitation substitutes," so they apply to all three. In short:

  • "Diamond" is reserved for diamond. Under 16 CFR 23.12(b), it's unfair or deceptive to use the unqualified word "diamond" for anything that doesn't meet the FTC's definition. Moissanite and CZ don't, so a "moissanite diamond" or "CZ diamond" description misleads.
  • Laboratory-grown diamonds need a qualifier. A laboratory-grown diamond meets the definition, but under 23.25(b) the stone's name must be immediately preceded, with equal conspicuousness, by "laboratory-grown," "laboratory-created," "[manufacturer name]-created" or a similar phrase that discloses it isn't mined. Under 23.12(c)(3), "cultured" is allowed only with that kind of clear disclosure.
  • "Laboratory-grown" can't stretch to imitations. Section 23.25(c) says it's unfair or deceptive to use "laboratory-grown," "synthetic" or similar words with the name of a natural stone unless the product "has essentially the same optical, physical, and chemical properties as the stone named." A laboratory-grown diamond qualifies. Moissanite or CZ sold as a "lab diamond" doesn't.
  • Imitations must say so. Section 23.25(b) requires words like "imitation" or "simulated," with equal conspicuousness, when a gem name or the word "stone" or "gem" describes an imitation. The FTC adds that "faux" alone is not an adequate disclosure.
  • No "real" or "genuine" for manufactured products. Section 23.27 makes it unfair or deceptive to use "real," "genuine," "natural" or "precious" for any product "manufactured or produced artificially."

How to make sure you get the stone that's described

  1. Read the product name. A laboratory-grown diamond listing should say "laboratory-grown" (or a similar term) next to the word diamond. A moissanite or CZ listing should name the material or say simulated or imitation.
  2. Find the report. Each of our stones comes with an IGI or GIA laboratory-grown diamond report. IGI says it screens every stone "to determine naturally mined, laboratory grown or simulant origin." A report that identifies moissanite is not a diamond grading report: IGI, for example, has issued certificates that verify a stone as lab-grown moissanite and state its shape, weight and colorless characteristics.
  3. Verify the report number on the lab's website and match the measurements and weight to the listing. Our guide to reading an IGI lab-grown diamond report, line by line shows where each detail sits, and IGI certification explained covers verification.
  4. Check the laser inscription. IGI says every laboratory-grown diamond it reports on has the prefix "LG" laser-inscribed on the girdle ahead of the report number; a jeweler with a loupe can match it to the report.
  5. Watch the video. A 360° video won't identify a material on its own, but it shows the stone's actual face-up look, which is what you'll live with.

Frequently asked questions

Is moissanite a lab-grown diamond? No. Moissanite is silicon carbide, a different material. GIA and IGI both classify it as a diamond simulant. It can be grown in a laboratory, but that makes it laboratory-grown moissanite, not a laboratory-grown diamond.

Is cubic zirconia the same as a lab-grown diamond? No. Cubic zirconia is zirconium oxide, a diamond simulant. GIA rates it 8.5 on the Mohs scale versus 10 for diamond, and notes that colorless CZ may yellow over time. A laboratory-grown diamond is diamond, with the same properties as a mined one.

Which is harder: lab-grown diamond, moissanite or CZ? Diamond, at 10 on the Mohs scale, whether laboratory-grown or mined. GIA rates synthetic moissanite at 9.25 and cubic zirconia at 8.5. GIA says diamond is harder than any simulant.

Does moissanite sparkle more than a diamond? It shows more colored fire. GIA says moissanite has more than twice the fire of diamond and slightly more brilliance, and that in larger sizes its intense fire may give it away as a non-diamond. Whether that look appeals is a matter of taste.

Can a diamond tester tell lab-grown diamond from moissanite? Not reliably. IGI warns that thermal testers can read moissanite as diamond, and electrical testers can mistake some laboratory-grown diamonds, particularly HPHT-grown ones, for moissanite. A gemological laboratory report is the reliable way to confirm what a stone is.

Can moissanite or CZ be sold as a diamond? No. Under the FTC Jewelry Guides, the word "diamond" is reserved for stones that meet the FTC's definition of diamond. Imitations must be clearly disclosed with words such as "imitation" or "simulated."

Browse our white laboratory-grown diamonds, round stones or every stone in the catalog. More guides are on our diamond guides page.

Sources

Reviewed October 30, 2026 against the sources above. The FTC Guides are guidance, not a substitute for legal advice.

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