How to Tell if Diamonds are Real

First and foremost, when purchasing a diamond, make sure it comes with a certificate. You want the certification to come from an impartial diamond grading authority such as GIA, AGSL, EGL, PGGL. The certification can also come from an independent appraiser who is affiliated with a professional organization. You never want to buy a stone site unseen (such as from the internet) without a valid certification from a reliable source.

Diamonds have a high refractive index and therefore, they sharply bend light that passes through them. Whereas, glass and quartz have a low refractive index and, therefore, sparkle less because they bend light less. Therefore, look through the stone to evaluate how light passes through it.

Unmounted Stones
If the stone is not mounted, turn it upside down and place it on a piece of newspaper or a book. If you can read the print through the stone or if you see distorted black smudges, the stone is likely not a diamond.

If the stone shows signs of double refraction, it may be Moissanite. Moissanite is a gemstone with many characteristics that mimic diamonds and frequently even jewelers have difficulty differentiating between diamonds and Moissanite.

Another tip is to draw a small dot on a piece and place the stone over the center of the dot. Look directly down on it, if you see a circular reflection in the stone, the stone is not a diamond.

Mounted Stones
If the stone is mounted, you should not be able to see the bottom of a diamond looking directly from the top.

Use a carat or gram scale to compare the weight of the stone to the weight of a real diamond of similar size. For example, cubic zirconia weighs about 55% more than real diamonds that are the same shape and size.

A real diamond will likely not be set in cheap metal, whereas a fake stone may be set in cheap, immitation metals. Stamps inside the setting that indicate real gold or platinum include: 10K, 14K, 18K, 585, 750, 900, 950, PT, or Plat. Furthermore, a "C.Z." stamp will immediately give away that the center stone is not a real diamond.

Try putting the stone under a UV light. Many diamonds will exhibit blue fluorescence under an ultra violet light. The presence of a medium to strong blue confirms that it is a real diamonds. Remember though that the absense of blue does not mean it is fake; higher quality diamonds do not exhibit blue fluorescence. If you see a very slight green, yellow, or gray fluorescence under the UV light, the stone may be Moissanite

Test the stone with a heat probe. Real stones disperse heat quickly and won't heat up with a heat probe. This takes about 30 seconds and does not hurt the stone in any way.

Real diamonds do not show up on an x-ray but glass, cubic zirconium and crystals all have slightly radiopaque quailities and show up on an x-ray.

Use a jeweler's loupe to inspect the diamond. Mined diamonds usually have small imperfections or inclusions whereas cubic zirconium does not have imperfections. Also, lab-grown diamonds--which should pass the other tests--usually don't have imperfections either.

If the stone is real it will sink and if it is fake it will float.

Put the stone in your mouth and breathe on it. If the stone stays "foggy" for 2-4 seconds it is not real. Real diamonds will have cleared by the time you look at them.