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How to Tell if Diamonds Are Lab Grown, Natural or Fake

Is your diamond a diamond? Is it a lab-grown diamond or a mined diamond? Is it a simulated diamond? Or just a fake?

It’s one of the first questions customers ask before deciding to buy a lab-grown diamond for an engagement ring or an important piece of jewelry.  How do you tell the difference between natural diamonds and lab diamonds?  Will people know what your diamond is just by looking at it?  Will your jeweler be able to tell?

How do you make sure that you know what you’re getting  (and that you’re getting what you’re paying for)?  These are all good questions.  Here are the differences between natural diamonds, lab-grown diamonds and simulated diamonds and how to tell that your diamond is really a diamond.

Diamonds vs Lab Grown Diamonds

Natural Diamonds vs Lab Diamonds: How to Tell

No one can tell just by looking at a diamond whether it is natural or lab created. You and your friends and family won't be able to see any difference at all. Jewelers can't see any difference with a loupe or microscope. No simple diamond tester will be able to tell the difference either.

That’s because there actually isn't any difference. Lab grown diamonds are diamonds, with the exact same physical, chemical and optical properties as mined diamonds. Because natural diamonds form deep in the earth and man-made diamonds are grown in a lab there are subtle differences in the microscopic crystal growth structures. Lab-grown diamonds and natural diamonds can have differences in their absorption spectroscopy, microscopic metallic inclusions, and fluorescence and phosphorescence but you need advanced detection equipment and training to detect them.

That’s why you need to rely on lab reports to certify the origin of your diamond. Both the Gemological Institute of America, GIA, and the International Gemological Institute, IGI, issue reports for both natural diamonds and lab grown diamonds. They grade both using the same quality scale and clearly identify whether a diamond is natural or lab-grown.

Most jewelers screen their diamonds using an interesting difference between most lab-grown diamonds and most natural diamonds. Most fine quality lab-grown diamonds are grown by the CVD process and are remarkably pure. They are rare Type IIa diamonds with almost no trace minerals at all. Only 2% of natural diamonds are Type IIa.  Most natural diamonds are Type Ia, which means they contain trace amounts of nitrogen, the impurity that gives diamonds a yellow hue.

For about $5000, jewelers can buy an advanced testing machine to see if the diamonds they buy are Type IIa and if they are, they can send them to GIA or IGI for further gemological testing to see if they are lab-grown or the rare pure natural Type IIa.

Video of Diamond vs Moissanite

Diamonds vs Moissanite: How to Tell

Moissanite is lab-grown silicon carbide. It is highly thermally conductive so it’s manufactured for electronics purposes. A manufacturer in North Carolina that specializes in growing silicon carbide crystals realized that they would make a good synthetic gem material. The crystals are usually greenish but they developed near colorless material to use as a diamond imitation.

Of course, moissanite isn't diamond, it’s silicon carbide. But it does have some characteristics that are similar to diamond. It has a higher refractive index than diamond so its facet pattern looks different. It has very high dispersion, breaking apart light into spectral colors. This creates a “disco ball effect” with more rainbow flashes than diamond, against an overall darker background. Jewelers and anyone else who sees a lot of diamonds will notice the difference immediately and know that moissanite is not diamond.

Because moissanite is thermally conductive, the inexpensive diamond tester pens that were developed to quickly test and identify other imitations that don't have any thermal conductivity don't work for moissanite. You need a more precise detector or you can use standard gemological testing for standard properties like refractive index, specific gravity, dispersion and birefringence, all of which are different in diamond and moissanite.  In particular, moissanite is doubly refractive, so you will see doubling of the facet junctions under magnification. You will see this as a slight blurriness of the facet pattern with the naked eye that’s a sure indication that a gem is not a diamond.

Diamond will scratch moissanite but this isn't recommended as a test since it damages the moissanite. Moissanite’s hardness of 9.5 sounds like it is similar to diamond’s hardness of ten on the Mohs scale but diamond is actually more than twice as hard: moissanite has a Knoop Hardness of 3000 and diamond has a Knoop hardness of 8000.

Cubic Zirconia

Diamonds vs CZ: How to Tell

Most of the imitation diamonds you encounter will be cubic zirconia: a lab-grown diamond imitation that doesn't occur naturally. The cubic form of zircon oxide isn’t stable at room temperature but scientists found a way to make it stable by adding calcium or yttrium oxide.  That means the recipe for CZ isn't always the same and CZ made by different manufacturers will have slightly different properties.  Some CZ may become more yellow or cloudy over time and have to be replaced. CZ is much less expensive than diamond, lab diamond or even moissanite.

But because CZ is so inexpensive, about $10 for a 1-carat stone, you can easily replace it. CZ is usually set in costume jewelry with base metal and inexpensive fun jewelry styles. It’s not as desirable for meaningful jewelry that you want to keep and wear for a long time, particularly rings, because it may get damaged and have to be replaced.

Sometimes CZ is sold under brand names as a “diamond simulant: and not identified as CZ.  This is legal as long as the company is clear that it is not a diamond or lab-grown diamond. The U.S. Federal Trade Commission sent warning letters to several companies for being unclear that they are selling CZ, not lab-grown diamond.  If you see the word “simulant” in a jewelry description, the stone in the jewelry is NOT a diamond or lab-grown diamond, it’s an imitation. It’s a cleverly marketed fake.

It’s very easy to tell the difference between diamond and CZ with a very inexpensive thermal conductivity tester. If it buzzes, it’s diamond.  If not, it’s probably CZ or glass or some other inexpensive imitation.

Swarovski crystal, synthetic colorless sapphire, and earlier generation imitations like YAG (yttrium aluminum garnet) may also be seen imitating diamond in class rings and vintage jewelry.