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The Difference Between a Diamond and Cubic Zirconia - HQ Insider
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The Difference Between a Diamond and Cubic Zirconia

How to tell a diamond vs cubic zirconia

The Difference Between a Diamond and Cubic Zirconia

I have heard it many times that a diamond is a girl’s best friend, but I have never heard that about CZ.  So how can you tell you are getting what you pay for? How do you tell the difference between a diamond and a cubic zirconia?

To the naked eye a diamond and cubic zirconia almost look exactly the same.  The most conclusive way to tell the difference between the two is with an electronic device that reads the stones electrical and thermal conductivity, but you can also conduct some of these below tests at home to see whether or not you have a real diamond.

Diamonds are harder than CZ

Diamonds have the hardest, naturally occurring surface, so they shouldn’t be able to be scratched or cracked easily. On the Mohs scale of hardness, a diamond ranks the highest at 10. CZ is 8.5.  There are two tests you can conduct to determine whether a diamond is real or not. The first test involves rubbing sandpaper over the stone, if it scratches, then it is a cubic zirconia. A diamond wouldn’t be scratched by the roughness of sandpaper. The second test involves heating the stone. Cubic zirconia is not as resistant to heat as diamonds and can easily crack and burn under high temperature (do this with caution).

Diamond and CZ scratch test
Diamond and CZ scratch test

Diamonds refract light and CZs do not

One of the most time- honored tests used by gemologists is still one of the most effective, place the stone on a newspaper (assuming the stone is lose) – because real diamonds refract light, it is impossible to read letters through it.  With many CZs you’ll be able to make out the letters through the stone.

Diamond and CZ newspaper test
Diamond and CZ newspaper test

Diamonds (usually) have flaws

One of the most important differences between CZs and diamonds is that cubic zirconia is virtually flawless. Since CZs are created artificially, they won’t have any inclusions. If you have a loop at home, take a look at the stone to see if there are any inclusions to determine if you are dealing with a real diamond or not.

CZ is heavier than a diamond

Cubic Zirconia also weighs more than a diamond. If you have two stones that are approximately the same size and one is a CZ and one is a diamond the CZ will be noticeably heavier (about twice as heavy).

CZ is heavier than diamond
CZ is heavier than diamond

CZ does not conduct heat as well

Lastly, cubic zirconia is a better thermal insulator than a real diamond.  Since diamonds have a higher thermal conductivity, if you breathe on a stone, the fog of your breath will disappear right away.  If you do the same test with a cubic zirconia, the stone will remain foggy for a longer time, indicating that you are not dealing with a real diamond.

So the next time you wonder if you’re looking at a real diamond, think about the above differentiators to see how you can tell the difference between a diamond and cubic zirconia and go ahead and conduct a few of those tests yourselves. Of course the safest way to determine whether a diamond is real or not is to have a certified gemologist take a quick look at it.

Missed the first post in the diamond series? Read about Diamonds and the 4 C’s here.  Interested in some of our exclusive finds? Check out Beverly Hills Elegance and EFFY!

Melissa Miner
Melissa Miner - Graduate Gemologist, G.I.A

Melissa Miner is a Graduate Gemologist from the G.I.A, one of the most recognized titles in the diamond industry. They are trusted experts for accurately identifying and grading the unique characteristics of diamonds and colored gemstones. Melissa has logged over 20,000 hours of live TV in the home shopping industry! She has a broad product category adeptness, but her favorite is the jewelry category presenting exquisite gemstones and diamonds.

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