How to Tell If a Diamond Is Real: The Complete Guide

You are getting engaged and have spent thousands of dollars on a diamond – but then you start having doubts about its authenticity.

An awful thought occurs to you.

What happens if it is a fake? After all, it is not as if this is an everyday purchase.

An engagement ring has far-reaching significance and meaning. If you start out your lives together with a fake ring, what does this imply about your future?

Hold on, though. Before you start reading all kinds of unnecessary symbolism into this disastrous scenario, let us help you by outlining the differences between real and fake diamonds and give you some tests you can do at home to allay your suspicions.

You are probably not a diamond appraiser or professional jeweler, so one diamond may look much the same as another.

How can you possibly tell if you’ve been cheated?

There are plenty of disreputable diamond sellers out there looking to make a fast buck at your expense.

If you’re not familiar with a diamond’s structure and components, you may be sold unwittingly a cubic zirconia or another diamond simulant, so it’s important to know how to spot a fake.

Only Buy from Trusted Retailers

Firstly, where you buy your ring makes a huge difference. If you bought your ring from a trusted retailer, you have absolutely no reason to be concerned about its authenticity.

You should look online, yes, but we stand by our recommendation of buying only through trusted names such as James Allen, Blue Nile and Brian Gavin.

These are highly reputable, honest retailers who offer third-party verified diamonds which have been tested for their 4Cs of quality – color, cut, clarity and carat weight by the Gemological Institute of America (GIA) or the American Gem Society (AGS).

When you buy through one of these online retailers, you will receive a certificate showing the quality, and therefore the authenticity of your diamond.

Still having doubts? If you are the suspicious type – even with a certificate in hand – how do you know for sure it is real?

Types of Fake Diamonds

“The biggest misconception is there’s just one type of fake. There are several diamond substitutes and simulations on the market. Some of these substitutes have value in their own right—others are completely worthless,” says Shannon Delany, director of communications for James Allen.

Here are some basic differences between real and fake diamonds:

  • Real diamonds are much heavier and have higher density than most fake ones, although cubic zirconia is heavier than diamond.
  • Real diamonds are made from carbon, fake ones from glass and silicon.
  • Real diamonds refract light more than fake ones; images seen through diamonds are obscured but fake diamonds look clearer and more transparent.
  • Real diamonds have sharp edges. Fake ones will have rounded edges.
  • Real diamonds have imperfections; fake ones have none.
  • Real diamonds emit a blue glow in ultraviolet light; fake diamonds emit a yellow glow.
  • Real diamonds are less sparkly; fake ones look like high-end glass.
  • Check the setting. Does it have a gold (10K, 14K or 18K) or platinum mark (PT or Plat)? If the stone is fake it will probably not be set in a high-quality precious metal. If it is a cubic zirconia it should have a CZ marking.

Useful Tip

It’s much easier to test a loose diamond or one that hasn’t been mounted in a setting, so that you can verify its authenticity and determine if there are any flaws. Mounted diamonds can easily hide flaws or cracks and they usually reflect light into the diamond, which makes it difficult for anyone but a professional jeweler to assess its clarity or color. If you are buying a mounted ring, you can ask the retailer to remove the stone or have it appraised before it is mounted and while it is loose.

At-Home Methods to Determine If a Diamond Is Real

If you don’t want to enlist the services of an expert, at least yet, we’ll tell you about some home tests you can do to tell if you have a real diamond or not, plus other ways to authenticate your stone.

Read-through Test

Try and read a newspaper through the diamond. If it is real, you won’t be able to read a word. A fake diamond will let you read the words.

Water Test (if your stone is loose)

Fill a glass with water and drop the stone to the bottom of the glass. If it sinks, it is real. If it floats on the top or near the surface of the water, it is a fake.

Sparkle Test

Natural diamonds have a greyish sparkle to them. Fake stones such as cubic zirconia emit a highly colored, iridescent sparkle.

Breath Test

Breathe on the stone and see if it fogs up. If it does, and the fog goes away immediately, it is likely a real diamond. If it takes several seconds to clear, it is probably fake. Diamonds are able to quickly disperse the heat from your breath.

Dot Test

Draw a dot on a piece of white paper. Put the stone onto the dot, flat side down. If you can see the dot through the pointed end of the stone, it is fake. If the dot is not visible, the stone is real. This is because a real diamond refracts light which bounces off in different directions instead of in a straight line. 

Heat Test

Hold the stone with a set of plyers and heat it up under a flame for 30 to 45 seconds. Drop it into a glass of ice-cold water. If the stone shatters, it is probably a cubic zirconia or another fake type of diamond. Diamonds are among the strongest substances on earth, so they can easily withstand extreme changes in temperature.

Diamond Thermal Conductivity Tester/Probe

This is a relatively inexpensive tool you can buy on Amazon or eBay for as little as $20. It tests the thermal conductivity of your stone and will tell you if it is a real diamond or not. Diamonds are very effective heat conductors so when heat is transmitted through the tester it will disperse quickly if it is an authentic diamond. If the heat is dispersed at a slow rate, the diamond is not real. The tester has a needle-like tip that you place against the stone which beeps or indicates on a display if you have a real diamond.

Synthetic moissanite stones often have similar heat disbursement levels as diamonds, so if you want to be 100% sure, there are thermal conductivity testers that can tell the difference between diamond and moissanite. Presidium makes a diamond and moissanite tester which can tell the difference between the two. (At the writing of this article, Amazon had one priced at $399)

Black Light Test

Here is another test, which we should stress, is not as reliable as other methods of authentication. When you place a real diamond underneath an ultraviolet light, most of them, but not all, will turn blue. A fake diamond, on the other hand, will rarely look blue under a black or UV light.

Professional Methods

Not satisfied yet? If you would rather rely on a professional to tell you the truth – and you trust them, of course – there are several methods they will employ to examine your stone to tell you if it is real or not.

Inspecting a Diamond with a Loupe

The first thing a diamond professional will do is to look at your stone through a loupe. This is a special magnifying glass for examining all types of jewelry and it will show any blemishes or imperfections within the stone. No doubt you will hope he does not to find any – but, in fact the opposite is true. Fake diamonds will have NO imperfections, but real ones will have small inclusions deep inside the stone because they have been made by nature and are rarely, if never, completely blemish free.

Using a Scale

 Your gemologist will have an accurate, fine-tuned scale for measuring minute differences in carat weight. You’ll be surprised to learn that if your stone is a cubic zirconia, it will weigh almost twice as much as a similar sized diamond. That seems counter intuitive, but it is true.

Electricity Conductivity

Your jeweler or gemologist can also test your diamond with an electricity conductivity test using specialized testing equipment. Diamonds conduct electricity better than other stones, including synthetic moissanite and cubic zirconia.

X-Ray Testing

To analyze the internal qualities of a stone in detail, a professional diamond laboratory can test it for you. Their x-ray machines will be able to tell if the stone has a radiolucent molecular structure or a radiopaque molecular structure. Diamonds are radiolucent while fakes like cubic zirconium and crystals have more radiopaque features.

Common Gemstones That Look Like Diamonds

Let’s look at some of the diamond simulants, fakes and replacements, how they differ and how to tell them apart from the real thing. Diamonds have several “fake” counterparts that can easily be mistaken for real diamonds. Natural gems with a strong resemblance to diamonds are colorless sapphire, colorless topaz and colorless zircon. There are also gems created in a lab, like moissanite, cubic zirconia, YAG (yttrium aluminum garnet) and GGG (gadolinium gallium garnet).


Moissanite is often used as a substitute for diamonds and while it’s perfectly acceptable to have a moissanite ring, if you’ve been told it is a diamond and you’ve paid for a diamond, you might want to know what it really is.

Moissanite is a type of silicon carbide and it is fairly rare in nature, so most of it is man-madeina laboratory. It looks very similar to diamond so you may not be able to tell the difference. It has a Mohs scale rating of 9.5, which is very close to the hardness of a diamond (Mohs scale rating of 10)

  • Moissanite has more brilliance, sparkle and fire than a diamond.
  • If you look through the top or side of it, the facets on the opposite side will appear doubled. This is called double refraction and it does not occur in a diamond.
  • Moissanite weighs less than a diamond.
  • It is much cheaper than a diamond, costing 10-15% of a real diamond with similar 4C qualities.
  • Moissanite has higher clarity than a diamond, because most of it is man-made.

If you are still unsure, a special moissanite tester will let you know by passing electricity through the stone and seeing how it is conducted.

Cubic Zirconia

Cubic Zirconia is the cubic crystalline form of zirconium dioxide and it is made in a laboratory. It is one of the easier fake diamonds to test for authenticity. CZ, as it is usually called, is the most common and cheapest form of diamond simulant and you’ll find it in all types of jewelry.

  • CZ sparkles, with iridescent, orange and blue flashes of brilliance.
  • CZ is colorless, most diamonds have some degree of coloration.
  • CZ weighs more than a real diamond.
  • CZ has no imperfections or inclusions – as it is artificially made.
  • CZ takes longer to warm up in your hand than a real diamond as it transfers heat slowly.
  • CZ is much cheaper than a real diamond (approximately $20 vs. $1500 for a real diamond)
  • CZ can scratch and become cloudy over time, so it needs more care.

Colorless/White Sapphire

While still a precious gem and has much more value than CZ, for example, white sapphire is not a diamond. Sapphire is made of corundum and it comes in a range of colors including blue. White or colorless sapphires are sometimes mistaken for diamonds, but there are many differences between two.

  • White sapphires are generally duller looking than diamonds. Some are cloudy or milky.
  • White sapphires have less sparkle and lower light refractive properties.
  • White sapphires need regular cleaning as everyday dirt can dim their sparkle even more. 
  • White sapphires are not judged by their cut grading as they do not sparkle or emit fire. Instead it is their white coloring, shape and weight that determines their value and price.
  • White sapphires score a 9 on the Mohs Hardness scale, making them slightly more prone to scratching than a diamond.

Note: Both sapphires and diamonds can be artificially produced, and it takes an expert to tell the difference. If authenticity is key to your purchase decision you will want to know this upfront.

Colorless/White Topaz

Topaz comes in many colors including green, blue, yellow, orange and red. In its purest form, though, it is colorless. Topaz is a natural gemstone and is abundantly available.

  • Topaz loses its sparkle over time as it can easily accumulate scratches.
  • Topaz has a Mohs rating of 8, so it is considerably less durable than a diamond.
  • Topaz has more internal inclusions than diamond; the larger the topaz, the lower the price because there are likely to be more blemishes.
  • Topaz is much more affordable. A high quality 1 carat white topaz will cost around $100; a similar quality D color diamond will cost about $15,000.

Colorless/White Zircon

Zircon (not to be confused with cubic zirconia) is a natural gemstone found in Sri Lanka, Cambodia, Brazil, Africa and Australia. When it is pure, it is colorless and is therefore often a substitute for diamond.

  • Zircon almost rivals a diamond for fire and brilliance, when it is well cut.
  • Zircon is natural, therefore considered more desirable than CZ or other laboratory made simulants.
  • Zircon registers 7.5 on the Mohs scale, so it is not as durable as a diamond.
  • Zircon gemstones can darken after prolonged exposure to sunlight. Heat treatment can reverse this.
  • Zircon is prone to chipping and cracking.
  • Zircon needs to be faceted carefully to prevent blurry lines – as it has strong double refraction properties
  • Zircon is cheaper than diamond, but more expensive than CZ, for example. It can cost anywhere from $50 – $400 per carat depending on its quality.


YAG or Yttrium Aluminum Garnet is a laboratory made gem which was originally develop for use in laser and eye surgery in the 1950s, but later became an alternative to diamond. Its production for jewelry was reduced after the introduction of CZ, so you will not find much of it around.


GGG or Gadolinium Gallium Garnet is also laboratory made. It was an early substitute for diamond and is a lot denser than diamond but much softer (6.5-7.5 on the Mohs scale). It is available in colorless to light brown to yellow – and can turn brown with UV light exposure.

Synthetic/Lab-Grown Diamonds

We now need to look at synthetic or laboratory-grown diamonds. Aren’t they “fake?”

Well, no. Synthetic diamonds are man-made, yes, but they have similar molecular, optical and chemical characteristics that natural ones do.

Technically, therefore, they are real diamonds. Laboratory grown diamonds mimic the conditions that produce natural diamonds; that is – high pressure and high temperature.

Laboratory grown diamonds are categorized as either high-pressure, high-temperature (HPHT) or chemical vapor deposition (CVD) diamonds, depending on the method of their production.

Here’s a comparison showing their differences and similarities:

Both synthetic and natural diamonds have flaws which affect their 4C clarity grading.

Lab-grown diamonds come in limited colors, including white, yellow, blue, pink and green with color grades ranging from D to K. Organic diamonds can come in every imaginable color density and variation. Most common are white and the rarer are fancy yellows, pinks and blues.

Natural diamonds can take from 1 – 3.3 billion years to form underground, hence their mystique and perceived value. Synthetic diamonds can be made in6-10 weeks!

Synthetic diamonds are generally only available up to 20 carats in weight. Organic diamonds have been found as large as 400 carats and more.

Synthetic diamonds can cost up to 35% less than natural diamonds of comparable size and quality. That’s a big difference, however….

…the re-sale value of a lab-grown diamond is next to nothing. A real diamond should retain upwards of 30% of its original cost, depending on its 4C qualities. You will not be able to sell your synthetic diamond for anywhere near its original cost.


We’ve given you several ways to check your gemstone at home to see if you can tell if it is real or not and looked at the different “fake,” synthetic and simulant diamonds there are available today.

In all honesty, though, it is far better to consult an expert. Find someone with a Graduate Gemologist degree who can tell you for sure if your diamond is real or not. He or she has the expertise and professional tools to verify its authenticity and match it against your GIA or AGS certificate.

It is worth your peace of mind.