Stones like cubic zirconium, white topaz, and lab grown diamonds that look deceptively similar to the real thing can, and often do, confuse the untrained eye.

However, once armed with a bit of knowledge it will be glaringly obvious which doppelgänger is actually a phony.

Fortunately there are a variety of ways to make certain which one you’re dealing with. Don’t get had and spend thousands on a fake! Follow these industry insider tips to help you decipher when you have a real diamond on your hand (or neck or ear, etc.)

Check Its Brilliance and Fire

Non-industry folks are often confused about the rainbow spectrum emitted from real and fake diamonds. While both do display those colors to varying degrees, the trick is to take a close look inside the stone. If it shines in white and grey scale, and produces rainbow flares externally, you are probably dealing with a real diamond. This light that’s cast outwardly is know as its “fire”. If, however, you see the colors of the rainbow when you peer inside the stone, you are likely dealing with a fake.

Look for Inclusions and Imperfections

Diamonds are forged in the deep recesses of the earth. As such, real diamonds almost always contain carbon deposited imperfections known in the industry as “inclusions”. Under a loupe, a small magnifying glass that’s used to inspect jewelry, a fake stone will look nearly perfect, clear and free of any observable flaws.

Determine its Sharp or Rounded Edges

Using your loupe, you can also make note of the stone’s edges. Rounder looking edges indicate a fake while sharper edges are required to cut the dense gem material of a real diamond.

See if You Can Fog it Up

Because they’re so dense, diamonds don’t retain heat well. For this reason you’d have to breathe on them a while before the surface of the stone would begin to fog. Such is not the case with fake stones that will fog up almost immediately once your hot breath passes over.

Investigate Mountings and Settings

Most diamonds are mounted in lux settings like gold or platinum to keep them firmly secure and safe. After all, who wants to spend thousands of dollars on a real diamond only to have it etched with cheap plated-metal? When assessing the stone, take a cue from the surrounding metal that houses it.

Look for High Refractivity

Though they may look similar, brilliance and refractivity are very different. Real diamonds, which have a high refractive index, make it difficult to see through. Meaning that if you can look inside the stone and can see through to the mount, or if you have a loose diamond that shows the surface below it, you’re probably dealing with a fake diamond.

Conduct a Sandpaper Test

This one may seem like a no brainer, but since real diamonds are made from some of the hardest material in the known world (a 10 on the Mohs scale of mineral hardness), fake diamonds are easily scratched by sandpaper’s rough surface.

Consult a Geologist

Finally, the one true way to tell what kind of stone you have on your hands is to take it to a trusted geologist. Just be sure to find a qualified professional at some place like an antique shop as salespersons in chain stores may not have the proper education to discern real diamonds from fake diamonds.