When buying or inheriting a diamond, one of the most important questions you can ask is: is it real? Diamonds hold exceptional value, both emotionally and financially, so it’s no surprise that imitations and synthetics have become increasingly sophisticated. Whether you’re a first-time buyer or simply curious about a family heirloom, learning how to identify a real diamond can help you protect your investment and understand what you’re wearing. At Johnston Jewelers, we believe in transparency, education, and confidence with every purchase—and that starts with knowing the basics.
Real diamonds are made of pure carbon and form under intense pressure and heat over billions of years deep within the Earth. Because of their natural origin and hardness (they rank 10 on the Mohs scale), diamonds have several traits that are difficult to duplicate. However, modern simulants like cubic zirconia and moissanite, as well as lab-grown diamonds, often look similar to the untrained eye. That’s why it helps to know a few beginner-friendly techniques to evaluate whether a diamond is authentic.
First, there’s the fog test. Breathe on the stone as if you’re fogging a mirror. A real diamond will disperse heat rapidly and clear up almost immediately. Simulants tend to stay fogged for a few seconds longer. While not foolproof, this simple test gives you a quick clue.
Next, observe how the diamond interacts with light. Real diamonds reflect light in three unique ways: white light (brilliance), colored light (fire), and sparkle (scintillation). If the stone appears too “rainbow-like” or dull under direct light, it may not be genuine. Cubic zirconia, for example, tends to have a rainbow sheen that’s more artificial in appearance.
Try placing the loose stone over a newspaper or black dot on a piece of white paper. With a real diamond, the dense crystal structure and refractive index scatter light so strongly that you won’t be able to clearly read or see through it. If you can make out letters or dots through the stone, you’re likely dealing with an imitation.
Another test is hardness. Diamonds can scratch glass easily, while most imitations cannot. That said, moissanite—another hard material—can also scratch glass, so this test is useful but not definitive. Use caution with this method if the stone is already mounted.
Weight and feel can also be telling. Cubic zirconia is noticeably heavier than a diamond of the same size, while moissanite is slightly lighter. If you’re holding two similarly sized stones, the weight difference may be noticeable in hand.
Even though these at-home methods are helpful, nothing replaces professional verification. A certified jeweler can examine the stone under magnification, use specialized tools like diamond testers or UV lights, and confirm authenticity through grading certificates. One of the most reliable signs is a diamond grading report from a respected authority like GIA (Gemological Institute of America) or AGS (American Gem Society), which details the 4 Cs—cut, clarity, color, and carat weight—and confirms that the stone is natural or lab-created.
It’s also important to distinguish between natural diamonds and lab-grown diamonds. Lab-grown diamonds are real diamonds in terms of chemical and physical properties, but they are grown in a lab rather than in the Earth. They often cost less and are increasingly popular, but they must be disclosed as lab-created at the time of sale.
At Johnston Jewelers, we proudly offer only certified, conflict-free diamonds and are happy to verify or appraise any diamond brought into our store. Our in-house gemologists and experts can walk you through every aspect of your diamond’s identity—so you can buy, gift, or wear with confidence. When you shop with us, you’re not just buying sparkle—you’re buying trust, legacy, and expertise.