In A Nutshell
While one is obviously naturally formed and the other is a man-made impostor, telling the difference between the two can be difficult if you don’t know what you’re looking for. The most conclusive way to tell the difference is with an electronic device that reads the stone’s electrical and thermal conductivity, but you can also look at the surface of the stone for any tell-tale scratches (diamonds shouldn’t have any), the color of the stone’s refraction (the light of a diamond will refract gray), and for flaws that will suggest a naturally made stone. Other tests include breathing on the stone, putting it under a black light, and trying to scratch glass with it.
The Whole Bushel
To the naked eye, a diamond and a cubic zirconia can look exactly the same—that’s the idea, after all. But while it’s long been said that a diamond is a girl’s best friend, that’s absolutely never been said about a cubic zirconia. So how can you tell that you’re getting what you pay for?
With recent advances in the manufacture of faux diamonds, this is made a little more difficult. Some of the tests still stand, but as various stones share qualities with diamonds, it’s important to look at more than one aspect of the stone. In fact, some high-quality cubic zirconia can also pass some of these tests (such as the scratch tests) but generally cannot pass all of them.
Diamonds are the hardest naturally-occurring surface; as such, they shouldn’t be able to be scratched easily. That’s the first step. Take a look at the surface of the stone in question: closely. There shouldn’t be any surface scratches on it if it’s a real diamond. Then, try to scratch glass with it. This isn’t a foolproof test, as there are also some fake diamonds that can scratch glass, but it’ll give you a good idea on whether or not you need to keep going.
One of the most time-honored tests used by gemologists is still one of the most effective. Place the stone on a newspaper. Because a real diamond refracts light—a lot—it’s impossible to read letters through it. Many cubic zirconia you’ll be able to make out letters through.
Another easy test is to breathe on the stone. Diamonds don’t retain heat, so they’ll become almost instantly clear again. Cubic zirconia tends to retain heat longer than a diamond and will stay cloudy.
If you have access to a black light, take a look at the diamond beneath it. Real diamonds should turn blue. However, the brighter the blue, the less pure the diamond. Those of extremely high quality will, ironically, fail this test. A cubic zirconia won’t reflect a blue fluorescence.
Also, if you have access to a stone that you’ve already confirmed the properties of, it’s easy to compare weights between cubic zirconia and real diamonds. A cubic zirconia is about 50 percent heavier than a real diamond.
Make sure the stone is clean before conducting any of the tests. If there’s a film or dirt present on the surface of the stone, it can interfere with results.
It’s also important to note that there are two distinctly different types of diamonds. There are those that are formed naturally, beneath the earth, created from carbon dioxide that was subjected to an amazing amount of pressure. There are also diamonds that were made in a laboratory; these diamonds are, in all purposes, diamond. They’re not fakes in the sense that they’re not going to have all the same qualities as a stone made in nature. But if your heart’s set on a diamond that was made in nature, it’s worth asking some more questions about where exactly your stone came from.
Show Me The Proof
LiveScience: How to Test a Diamond
Abazias Diamonds: Tests to Tell Genuine Diamond from Cubic Zirconia
Gemesis: Lab-Created Diamond FAQ