Are Lab-Grown Diamonds Real? (And Do They Pass a Diamond Tester?)

Yes. A lab-grown diamond is a real diamond, and it will read as one on a standard diamond tester. The only thing that separates it from a mined stone is where it grew: one formed in the earth, the other in a machine, and everything after that is identical.

Yes, lab-grown diamonds are real diamonds

The cleanest answer to this is a legal definition rather than a marketing line. Under the federal Jewelry Guides at 16 CFR 23.12, a diamond is "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. Read that definition again and notice what is missing. Nothing in it mentions a mine, and nothing in it mentions how long the stone took to form. A stone either has that chemistry and that structure or it does not. Lab-grown diamonds do.

That wording is deliberate. The FTC revised its Jewelry Guides in 2018, and the definition of the word "diamond" was one of the twelve items it addressed. The same rules say a laboratory-created diamond has "essentially the same optical, physical, and chemical properties as mined diamonds." What sellers must do is disclose that the stone was not mined, using a plain term like "laboratory-grown." That rule exists so you know what you are buying, not because the stone is a lesser thing.

And if what you actually want is a stone that formed in the earth, that is a completely fair thing to want, and I would not talk you out of it. Some people care about the origin story, and the origin story is the one thing a growth chamber cannot reproduce. Liori sells both, so if that is you, go look at the mined diamond engagement rings instead. For the far more common worry, which is "did I just buy something fake," the answer is no, and the next section shows you why in one glance.

The four materials, side by side

Most of the anxiety around this question comes from lumping four very different things into one bucket. Two of them are diamonds. Two of them are not. This table sorts them out. It answers one question only, which is whether the stone is a diamond, and it is not a ranking of what you should buy.

Those hardness numbers come from GIA, which puts moissanite at 9.25 and cubic zirconia at 8.5 on the Mohs scale in its guide to imitation gem materials. A diamond sits at 10, lab-grown or mined, because hardness is a property of the crystal and the crystal is the same either way. That gap sounds small and is not: the Mohs scale is a ranking, not a ruler, and diamond is meaningfully harder than everything below it. It is the reason a diamond keeps its polish through decades of daily wear while softer stones pick up a haze of tiny scratches. If you want the grading vocabulary behind the rest of the report, our diamond color chart walks through what those letter grades mean.

Do lab-grown diamonds pass a diamond tester?

Do lab-grown diamonds pass a diamond tester? Yes. A pen-style tester measures how quickly heat moves through a stone, and a lab-grown diamond has the same carbon lattice as a mined one, so both read as "diamond."

Inside that pen the sequence is simple. The probe tip warms up and touches the flat top facet of the stone. Then it measures how fast that heat drains away. Carbon atoms locked in a diamond lattice pass heat along remarkably well, so the warmth disappears into the stone almost instantly and the meter swings to "diamond." A lab-grown diamond has exactly that lattice. There is no version of this test it could fail, because the test is asking about the material, and the material is diamond.

Cubic zirconia is the opposite story. Heat moves through it sluggishly, the meter never swings, and the tester says no. That is the honest "fake diamond" case, and it is exactly what a pen tester was built to catch.

Moissanite is the interesting one, and it is why better testers have two modes. Moissanite moves heat about as well as diamond does, so a heat-only tester will happily call it a diamond. Gemologists separate the two with a second test for electrical conductivity, which moissanite carries and diamond does not. You can see both tests in action in a GIA Gems & Gemology lab report, where a submitted stone read as diamond on thermal conductivity and only came apart under the electrical test. If someone is checking a stone for you with a single-mode pen, that pen can tell diamond from cubic zirconia but it cannot reliably tell diamond from moissanite. Our moissanite and lab diamond comparison goes deeper on how the two stones differ in the hand.

One limit worth knowing, because it trips people up: a diamond tester identifies the material, not the origin. It will confirm you are holding a diamond. It will never tell anyone whether that diamond grew underground or in a chamber. No handheld device does.

Moissanite and cubic zirconia: the actual look-alikes

Are lab-grown diamonds the same as moissanite or cubic zirconia? No. Those are different materials, silicon carbide and zirconium dioxide, not carbon, so they are not diamonds and they do not behave like diamonds under testing.

The trade word for these stones is "simulant." GIA defines a simulant as a material that looks like another gem and stands in for it, but has "very different chemical composition, crystal structure and optical and physical properties." That description fits moissanite and cubic zirconia. It does not fit a lab-grown diamond, which has the same composition and the same structure as a mined diamond rather than merely resembling one. This is the distinction the whole "is it real" question turns on, and it is why the FTC treats calling cubic zirconia a "laboratory-created diamond" as misleading.

The differences show up in the stones themselves, not just on paper. Moissanite throws more than twice the fire of a diamond, meaning far more rainbow flashes, which in larger sizes reads as showy rather than white. It is also doubly refractive, so looking through the top you can catch a doubled image of the back facets and the interior can seem slightly blurry. Cubic zirconia has more fire than a diamond but less brilliance, and GIA notes it tends to yellow over time. None of that makes them bad stones. Moissanite is durable and good-looking, and plenty of people choose it on purpose. It is simply not a diamond, and if you were promised a diamond, that is the difference that matters. For a fuller side-by-side, see our guide to choosing between the two.

Can a jeweler, or your family, tell?

Can a jeweler tell a lab-grown diamond from a mined one? Not by looking. GIA says ordinary gemological tools cannot separate them, and confirming origin means sending the stone to a laboratory for advanced testing.

This is the fear underneath most of the searches that land on this page, so let me answer it plainly. Across a dinner table, or on a hand in motion, there is nothing to notice. The stones return light the same way because they are the same material cut the same way. There is no telltale flash and no giveaway color, because there is no "lab-grown look" to spot in the first place.

The authority on this is blunt about it. GIA's guidance on how to identify laboratory-grown diamonds says the two are "essentially chemically and optically the same," so normal gemological tools "are not able to tell them apart." The lab needs purpose-built machines to make the call. A jeweler at a counter has a loupe and a pen tester. That is not enough, and no amount of experience makes up for it. What a jeweler can do is read the report and the laser inscription. That is not detective work, because the origin was published on purpose. If you want to understand what you are looking at before you buy, our guide to picking a loose lab-grown stone covers what to compare.

How a lab-grown diamond is made, in one paragraph

Knowing roughly how the stone came to exist makes the "is it real" question feel less abstract, so here is the short version. There are two production methods. High pressure, high temperature squeezes carbon under conditions that copy the deep earth. Chemical vapor deposition uses a carbon-rich gas in a vacuum chamber, where carbon settles layer by layer onto a thin diamond seed. Both grow a crystal, atom by atom, out of carbon. Neither coats, dyes, or fakes anything, which is why the result is a diamond rather than an imitation of one. The trade-offs between the two methods are a topic of their own, and our breakdown of HPHT and CVD growth covers which produces what.

How to check that yours is real

If you want certainty rather than reassurance, you do not need a gadget. You need the paperwork, and it is easier to read than it looks.

Start with the report itself, and check that it comes from a laboratory you have heard of rather than an in-house certificate written by the seller. Then find the origin line. GIA issues a dedicated Laboratory-Grown Diamond Report that states whether the stone was made by the CVD or HPHT method, and laser-inscribes the report number on the girdle, the thin edge running around the widest part of the stone. IGI, which has graded lab-grown diamonds since 2005, screens every stone it receives to establish whether it is mined, laboratory-grown, or a simulant, and inscribes lab-grown origin automatically.

That gives you a four-step check you can run yourself.

1. Find the report, and note which laboratory issued it.
2. Read the origin line. It names the growth method in plain words.
3. Look at the girdle under 10x magnification for the inscribed number, which GIA laser-inscribes on the lab-grown diamonds it grades.
4. Type that number into the laboratory's own database and check that the record matches the stone in your hand.

If all four line up, the question is closed. If a seller cannot produce a report from a recognized laboratory, that is the real warning sign. It is a far better thing to worry about than whether a diamond grew in a chamber. Our diamond certification guide explains how to read a full report line by line, and every stone in the GIA certified collection ships with one.

Frequently Asked Questions (FAQ)

The questions our consultants field most often from buyers weighing up a stone in the lab-grown collection.

Are lab-grown diamonds fake?

No. A fake diamond is a different material dressed up to look like one. That is what cubic zirconia and moissanite are. A lab-grown diamond is carbon, in the same crystal structure as a mined one. It is just as hard, and it bends light the same way. So it meets the federal definition of a diamond. The word for the difference is "origin," not "authenticity." If the comparison you actually want is against moissanite, our moissanite comparison lays it out.

Do lab-grown diamonds pass a diamond tester?

Yes. Standard testers work by measuring how fast heat travels through a stone, and a lab-grown diamond conducts heat exactly like a mined one because it is the same lattice of carbon. Both read as "diamond." Cubic zirconia fails that test, while moissanite can pass a heat-only tester and is separated out by a second, electrical test. Worth repeating: a tester confirms the material, never the origin. You can see what a certified stone looks like in the certified diamond collection.

Will a jeweler know if my diamond is lab grown?

Yes, but only by reading the paperwork or the laser inscription. Not by looking at the stone across a counter. GIA says ordinary gemological tools cannot separate the two, and that pinning down origin means sending the stone to a lab. So a jeweler can find out, because the report says so and the girdle is inscribed. That is disclosure doing its job, not a secret coming out. Our guide to reading a grading report shows where that line appears.

Do lab-grown diamonds sparkle the same as mined diamonds?

Yes, and for a boring reason: sparkle comes from how light bends and bounces inside the stone, which is set by the material and the cut. Both are identical here. What actually changes how much a diamond sparkles is cut quality, not origin, so a well-cut lab-grown stone will out-sparkle a poorly cut mined one every time. Moissanite is the stone that looks different, throwing noticeably more rainbow flashes. Cut and color grades are where your attention belongs, and our color grade guide is the place to start.

Are lab-grown diamonds worth less because they are lab grown?

They cost less to buy, and they resell for less. Those are two different facts, and they often get mashed together. Either way it is a pricing question, not an authenticity one, and it does not change what the stone is. We wrote a separate, honest breakdown, so rather than repeat it here, see what a lab-grown diamond is really worth on resale. If you are weighing the full buying decision between the two, our lab versus mined comparison covers quality and cost together.

Do lab-grown diamonds get cloudy or lose their sparkle over time?

No. Hardness is a property of the crystal, and a lab-grown diamond sits at 10 on the Mohs scale just like a mined one, so it resists the everyday scratching that dulls softer stones. What does happen to any diamond is a film of skin oil and soap on the underside, which flattens the sparkle until it is cleaned off. Warm water, a drop of dish soap and a soft brush fixes that. Cubic zirconia is the stone that genuinely degrades, yellowing as it ages. Browse stones that hold up in the engagement ring collection.