Cubic Zirconia VS Natural Diamonds

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A lot of buyers out there are surely familiar with the infamous Cubic Zirconia gemstones, also known simply as "CZ" by most in the trade. These little brilliant gemstones are pretty much always a result of man-made endeavors. The material itself is actually the cubic form of crystallised zirconium oxide. Scientists have noted that natural zirconium oxide was discovered in the year 1892, as the mineral called baddeleyite, however its yellowish form was hardly comparable to the brilliant CZ specimens manufactured by thousands of companies today.

CZ in its own right, is a brilliant gem that displays a very beautiful luster and vivid dispersion. Perhaps these traits are among the reasons why many people confuse CZ with diamond at first glance. The proper knowledge can help everyday people differentiate between these two stones quite easily, and therefore avoid being swindled by any dishonest merchants that don't fully disclose their product's actual identity.

So today, let us examine the property differences between cubic zirconia and the world's hardest gemstone; diamond.

First off, diamonds are much harder than CZ, with a Moh's scale rating of 10 versus 8. Most CZ stones are also packed together, so watch out for surface scratches and the presence of abrasion marks. This can be a hint that the stone you are viewing could be CZ rather than diamond. Usually diamonds of a half carat size or bigger,  are kept safe in individual containment cases. This prevents them from getting scratches from contact other diamonds.

Cubic Zirconia gems have a specific gravity rating that is about 1.7 times diamond's, thus they may feel slightly heavier when you bounce them lightly on your palm. Doing the specific gravity test using a hydrostatic scale would be a more accurate way to measure this property.

Many people notice how colorful CZ's dispersion can be when you rock and tilt a stone. What they don't usually know is that CZ's dispersion rate of 0.058 - 0.066 is actually higher than that of diamond's, which is at 0.044.

This doesn't mean that CZ is more beautiful, it simply tells us that more 'fire' can be seen when viewing CZ gemstones, especially under spot-illumination.

Fire is only one of the many factors that contribute to both gems' visual appeal. Diamond's luster is much stronger than CZ's because of its tightly knit atomic structure. This fact allows diamonds to reflect more light back to our eyes, hence making the reflections brighter and stronger. This trait is linked to the stone's superior hardness as well.

Diamond also has a refractive index value of 2.42, compared to CZ's RI of 2.15 to 2.18.
Most refractometers used in gemology cannot see these RI values in their scale (too high), however the difference in each gem's optical density can be observed using other methods.

CZ is the Most Commonly Known Diamond Simulant Today, Apart from Ordinary Glass. Its Properties Make it Difficult to Differentiate from Diamond, but Certain Tests Can Help You Tell if Your Stone is Actually a CZ or Something Else Entirely.


One easy-to-do test is called the read-through exam. This takes advantage of the different optical densities possessed by two different gem species. Placing a business card with 'small font' text (2 to 3 mm-tall text) under a faceted CZ stone will still allow you to make out the letters (although rounded significantly). Doing the same with a diamond will only show you a gray or murky area if you try to read the text through the gem. Do this with both stones pavilion up and observe the difference. Most people actually find this simple exam very useful for round brilliant cut stones, although of course there are always better scientific ways of separation done in a laboratory.

If you possess a microscope, you can check for an 'orange pavilion flash' on CZ stones by viewing them pavilion-up in darkfield illumination. On the contrary, diamonds will usually display a spectral-looking range of colors in this position, rather than an orange flash.

Some other simulants may be a bit more confusing though. Moissanite, Yttrium Aluminium Garnet and Diamond Coated CZ may all show a different result when subjected to these basic tests, so be vigilant and open to other conclusions.

There are many other ways of differentiating these two famous stones from each other, and from other common imitations as well. The fact also remains that newer and newer simulants are being discovered every day. Always be aware of this ever-present possibility, and stay curious in your journey to uncover more about the rewarding world of gemstones and gemology.

Gemcamp Laboratories

A Discovery Institute for Gemstones and Gemology

Our resident gemologists believe in encouraging public trust within the jewellery industry through shared education, value transparency and professionalism.

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