Cubic Zirconia

all colors
Photo date 4/02 © by J. Berg

by
Jessica Berg

my necklace
Photo date 4/02 © by J. Berg

Table of Contents

 orange cz
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Introduction

        Cubic Zirconia is well known as a substitute for diamond, due to its high hardness and great fire.  But in recent years, it has established itself as a gorgeous gem in its own right.  CZ is a beautiful synthetic gemstone that is durable and inexpensive and now even comes in any color of the rainbow, making it even more desirable.

        This web page was created to give you information regarding the synthetic gemstone, Cubic Zirconia, and to satisfy an assignment for Gemstones and Gemology, a course taught at Emporia State University under the instruction of Mrs. Susan W. Aber.    



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Physical Properties
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       Cubic Zirconia is a cubic form of zirconium oxide that is created in a laboratory, thus it is not a mineral.  However, it was found naturally occurring once at one site in the 1930's, but has yet to be discovered since then.  (Nassau, 1981)  The mineral with the same chemical composition as CZ, but in the monoclinic crystal system, is baddeleyite.  
     Cubic zirconia has a hardness of 8.5 on Moh's Scale of Hardness and a white streak.  It has a specific gravity between 5.65 and 5.95, and a density between 5.5 and 5.9.   (interlap.com)  It is in the isometric crystal system with a 4/mbar32/m crystal class and a Fm3m space group.   (Nassau, 1981)  The refractive index of CZ is between 2.088 and 2.176, which is very high.  It has dispersion in the C-F area of the visible light spectrum of 0.060.  (interlap.com)  Since CZ is transparent, it is often faceted.  It can be made in nearly any color and can be faceted into many cuts.

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Chemical Properties
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           Cubic Zirconia is an oxide of the metallic element zirconium, ZrO 2.  Each zirconium atom is surrounded by eight oxygen atoms and each oxygen atom is connected to four zirconium atoms.  Mostly all CZ on the market also contains yttrium oxide that acts as a stabilizer.  In colored CZ, other oxides are added to produce the colors.  Most CZ is about 87.5% zirconium oxide and 12.5% yttrium oxide.   (Nassau, 1981)  Though these compounds are both opaque, white ores, they melt together to form an amazing clear crystal.   (interlap.com)




Image scanned from (Nassau, 1981)

The Making of CZ

  Image scanned from (Nassau, 1981)

                                                                        
        To produce CZ, baddeleyite (ZrO2 ) is heated to about 2300 degrees Celsius (almost 5,000 degrees Fahrenheit).  This causes the mineral to become isometric.  However, this change is not permanent, it reverses upon cooling; which is why a stabilizer must be added to prevent transformation upon cooling.   If too much stabilizer is added, it results in a softer, less brilliant product.  (Nassau, 1981)  This requires such high heat that a special radio frequency "skull crucible" must be used to melt the zirconia powder.   (bodyjewels.net)  This apparatus is shown in the picture and diagram above; it consists of a cup-like arrangement made up of a circle of copper fingers that is water cooled by internal plumbing.  As the zirconia melts, it leaves a thin shell that remains  solid because it is cooled by the water in the copper fingers.  As this occurs the zirconia and the stabilizing oxide are added to fill the skull the the desired level.  The contents are kept molten for several hours to ensure uniformity.     (Nassau, 1981)  To produce colors, oxides of cerium, copper, titanium, iron, nickel, and many other elements are added also.


   

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Colored CZ
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         To produce colored cubic zirconia, the following oxides can be added to achieve the following colors.   (18carat.co.uk)

rough colored cz
Image scanned from (Nassau, 1981)

Oxide
Colors Produced
Cerium oxide
 red, orange, yellow
Copper oxide
 yellow, amber, brown
Iron oxide
 yellow, amber, brown
Nickel oxide
 yellow, amber, brown
Praseodymium oxide
 yellow, amber, brown
Titanium oxide
 yellow, amber, brown
Erbium oxide
 pink
Europium oxide
 pink
Holmium oxide
 pink
Chromium oxide
 green
Manganese oxide
 green
Vanadium oxide
 green
Cobalt oxide
 lilac, violet
Manganese oxide
 lilac, violet
Neodymium oxide
 lilac, violet
Excess yttrium oxide
 blue, green

History

        Cubic Zirconia was discovered in its natural state in 1937 by two German mineralogists, von Stackelberg and Chudoba.  It was in a highly metamict zircon given to them by B.W. Anderson.  The zircon contained tiny crystals that were determined to be the cubic form of zirconium oxide by x-ray diffraction.  The two mineralogists thought so little of their discovery that they did not even give it a name; which is why it is still known by its scientific name, cubic zirconia.  (Nassau, 1981)  It wasn't until the 1970's, however, that Soviet scientists learned how to grow the crystals in the laboratory.   (bodyjewels.net)  In 1977, it was first marketed under the trade name "Djevalite."   (18carat.co.uk)  But CZ really took off in the 1980's when Swarovski & Co., a world-renowned Australian producer of leaded crystal, began producing cubic zirconia for mass consumption.   (bodyjewels.net)


Caring for CZ

        Cubic zirconia can be cleaned with any conventional jewelry cleaner or detergent.  With such a high hardness and durability, you can use a brush to clean off dirt or oil also.  Ultra sonic jewelry cleaners may also be used on CZ and will not damage the stone.  However, when using soaps or detergents to clean CZ, one should wipe the jewelry dry thoroughly to avoid residue from the soap leaving a film that will dull the brilliance of the stone.  Cubic Zirconia should be cleaned frequently to remove oils from skin that also dull the brilliance of the gem.   (bodyjewels.net)



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Compared to Diamond
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        To the untrained eye, cubic zirconia looks identical to a good quality diamond, but CZ has slightly less brilliance or sparkle than a diamond and more fire or flashes of color.  The overall effect is so similar that it can even fool a trained gemologist on occasion.  One great difference between cubic zirconia and diamond is weight; CZ is about 75% heavier than diamond.  A piece of CZ the same size as a one carat diamond weighs about 1.75 carats.  CZ is also more brittle than diamond and softer.   (bodyjewels.net)  Cubic Zirconia is also flawless, whereas diamond usually contains impurities and inclusions.   (goldplace.com)


References

Nassau, Kurt, Cubic Zirconia:  An Update, p. 9-19 Gems & Gemology, Sp 1981
http://www.18carat.co.uk/cubiczirconia.html
http://www.bodyjewels.net/cubiczirconiainformation.html
http://www.goldplace.com/cubic.html
http://interlap.com/czgems/aboutcz.htm

  Please send questions or comments to Jessica Berg. This page was created on April 30, 2002.

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