There are lots of ways to test whether a diamond is real. You can scratch it, heat it up, or look at it through a microscope.
But can you tell whether a diamond is real at just a quick glance?
We reached out to diamond expert Russell Shor, the senior industry analyst at Gemological Institute of America, to tell us some ways diamonds differ from competitors in looks alone.
Notice the way light is refracting
Diamonds are so sparkly because of the way they refract and bend light. Glass, quartz, and cubic zirconia may mimic a diamond's brilliance, but they have much lower refractive indexes.
This means that if your stone isn't in a setting, you can place it over a newspaper and the light will scatter inside the real diamond and prevent a black reflection, according to Shor. A fake diamond will let the black type show through.
"If you can distinguish any of the letters by looking into the stone, it is not a diamond," Shor told Tech Insider.
If the diamond you're looking at is mounted, make sure you can't see through it to the mount — that's a sign the stone is most likely cubic zirconia or glass.
See how it sparkles in the light
The way diamonds reflect light is unique: Inside the stone, a high-quality diamond will sparkle gray and white — known as brilliance — and throw off flashes of color called fire.
Knowing this, it’s easy to tell the difference between a diamond and lesser stones. Take cubic zirconia (CZ) for instance. Not only will it have less brilliance than a diamond, but it will have less fire as well, according to Shor.
"A diamond has a higher refractive index than CZ, so diamonds will have more fire," he told Tech Insider.
Another popular diamond substitute is a stone called moissanite. Shor said moissanite is doubly refractive, which means it is way more sparkly than a diamond, with a lot more fire. In overhead or direct lighting, moissanite will often have a "disco-ball effect" and throw bright rainbow sparks in all directions.
To put it succinctly, a CZ gem will seem dull compared with a diamond and not nearly as sparkly. A moissanite stone will be way more sparkly than a diamond and give off a lot of fire or rainbow colors.
Still not sure? See an expert
Of course, this is all by glancing at a stone and not a definitive way to tell whether a diamond is fake or to distinguish between lab-grown diamonds and the real thing.
To be absolutely sure the stone you have is a real diamond, it is always best to consult a professional gemologist, Shor said.
But if you're just judging your friend's engagement ring, take a long hard look at how it sparkles.
