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Roger Weller, geology instructor

Cubic Zirconia
by Daniel Le
Physical Geology
Spring 2009


Diamonds vs. Cubic Zirconium

            Anyone who is familiar with gemstones (including myself) knows the “deal” with diamonds, both general and specific; how they are “a girl’s best friend,” the ideal gem for an engagement ring, one the hardest known natural substances in the world, one of the purest solid forms of carbon, are very beautiful and are very expensive (“very” being an understatement).  If a person is hoping to get their hands on a diamond, besides having 1-2 years worth of salary on hand, they need to what exactly what they are buying.  Due to the fact that diamonds are in fact very expensive and are increasingly harder to come by (in terms of mining them), more and more people are, either knowingly or unknowingly, buying a diamond-substitute substance called cubic zirconium, which has visual and physical properties similar to diamonds.  If one wants to buy a real diamond and not an imitation, they need to know what cubic zirconium exactly is and what their exact visual and physical differences are compared to diamonds.  This will be discussed as follows.

            Cubic zirconium (alternate spelling cubic zirconia) is the cubic crystalline form of the compound zirconium dioxide (ZrO2).  The mineral baddeleyite is the naturally occurring, albeit rare, form of this; it was discovered in 1892.  Laboratory-created cubic zirconium was discovered in the 1930’s by German scientists; the cubic zirconium that was created during this time was in miniscule amounts and it was deemed at the time to have no economic or real scientific value.  Commercial cubic zirconium was first developed during the 1970’s in Russia as a means to develop laser technology.  Cubic zirconium, as Robert James explains it:

…was made in Russia, for the purpose of laser technology. It seems the Russians did not have enough natural rubies that were required at the time to generate laser beams. So they set about to find a synthetic material that would have the properties of ruby. Their development: Cubic Zirconia. Not that CZ is particularly close to a ruby gemologically, but optically it served the purpose for the Russian laser technology (James).

           The website adds that, “In 1973, Soviet scientists at the Lebedev Physical Institute in Moscow perfected the technique of manufacturing cubic zirconia via the ‘Skull Crucible’ process” (Unknown).  Cubic zirconium is made by the heating of zirconium dioxide to the temperature of about 5,000 degrees Fahrenheit (approximately 2,300 degrees Celsius).  This would cause the compound to assume an isometric crystal form.  However, as Jessica Berg notes, “this change is not permanent, it reverses upon cooling; which is why a stabilizer must be added to prevent transformation upon cooling” (Berg).  This “stabilizer” would be minute amounts of either the element calcium or yttrium.  The result is the crystal block shown below:

Photo credit/copyright: Robert James


Cubic zirconium gems are then carved out of the crystal.


Photo credits: Roger Weller/Cochise College

Faceted cubic zirconium (left) and diamonds (right)


            At first glance, you and I would be hard pressed to find any visual differences in cubic zirconium gems compared to diamonds.  Fact is, there are visual differences with cubic zirconium and diamonds: they just require a magnifying lens and a very bright, high powered light source.  When observed under a microscope, diamonds have a so-called “dark spot,” an impurity which is the result of the presence of carbon that did not crystallize during the formation of the diamond.  Diamonds also tend to have a brown or yellow tinge to them when they refract light; this is due to the presence of nitrogen, which causes the impurity.  Due to its artificially created nature, cubic zirconium does not have any of the above impurities that diamonds potentially possess and always have a colorless or “white” appearance to them.  Additional tests reveal other visual differences between cubic zirconium and diamonds, one of them being that, as explained by, cubic zirconium “can take on a gray tone when exposed to sunlight for prolonged periods” (unknown), whereas diamonds do not.  For a technical aspect into the visual differences between cubic zirconium and diamond, a cubic zirconium capacity to disperse directed light or “refractive index,” is 2.176; a diamond’s refractive index is 2.417.  Thus, with these things in mind, one can establish the difference between a diamond and cubic zirconium with the naked eye.

Besides the visual differences, there are also notable differences in the chemical and physical properties of cubic zirconium and diamonds.  Diamonds, being the hardest substance on the planet Earth, has a hardness of 10 on the Mohs Scale of Hardness; cubic zirconium has a hardness of 8.5 on the same scale, therefore diamonds can scratch cubic zirconium but not the other way around.  Cubic zirconium leaves behind a white streak when rubbed on a streak plate.  Diamonds do not leave any streak behind; rather, diamonds would scratch the streak plate when rubbed against it.  Diamonds are thermal conductors, meaning that when exposed to an energy source, diamonds generate heat; cubic zirconium on the other hand, is a thermal insulator, meaning that it absorbs heat when exposed to an energy source.  Lastly, the specific gravity of  cubic zirconium is around 5.6 to 6 compared to diamond’s 3.5; subsequently, cubic zirconium has a heavier mass weight than that of diamonds; the website mentions that “a cubic zirconia will weigh about 1.7 times more than a diamond of equivalent size” (unknown). 

Now that the secrets behind what cubic zirconium exactly is have been revealed, you and I are now better prepared to make sure that the diamond either of us buys is the real deal and not an imitation.  The only thing we need to worry about now is clearing away the four or five thousand dollars need to clear the price tag.



Works Cited

Unknown.  “Cubic Zirconia vs. Diamond.” Unknown.  3 April 2009.

Unknown.  “Diamond Simulants: Cubic Zirconia.” Unknown.  3 April 2009.

Berg, Jessica.  “Cubic Zirconia.”  Emporia State University- Earth Science Department.  30 April 2002.  3 April 2009.

James, Roberts.  “The Study of Cubic Zirconia: The History of Cubic Zirconia.” Unknown.  3 April 2009.

Picture Credits

James, Roberts. April 2009.

Weller, Roger.  Cochise College.  April 2009.