Rough uncut diamonds are often confused with similar-looking materials such as cubic zirconia, moissanite and quartz. The easiest way to spot a real uncut rough diamond it to use a battery operated diamond tester. Testers can be purchased for about $90 and up and are very accurate in detecting genuine diamonds. The size of a tester makes it especially useful to prospectors, buyers, jewelers and pawn shop owners.
Let your stone sit at room temperature for 10 minutes without handling it.
Pick it up and put it close to your mouth. Exhale on the stone to “fog it up.”
Look at the stone and see how long it takes for the fog to clear. If it is 3 to 5 seconds or less your diamond is possibly real.
Place the stone on a newspaper if it is not completely cloudy. Try seeing the print through the stone. If you can read the print or see it clearly, the stone is likely a fake. This test can have mixed results if your stone is very cloudy.
Scratch the surface of a small compact mirror. A real diamond should have no trouble scratching your mirror. You can also try rubbing the stone with sandpaper. A real diamond should not be scratched. However, doing scratch tests can ruin otherwise beautiful cubic zirconia jewelry and is not recommended.
Take the stone to a jeweler if your tests prove inconclusive. A jeweler is your best and most accurate option and will tell you almost instantly if the stone is real or not. Often you can find a jeweler willing to check out your stone free of charge.
All of these tests can help you determine if your diamond is real but stone size and condition can cause conflicting or false results. A diamond tester should be used before purchasing a rough uncut diamond to avoid buying a fake.