What is a Cubic Zirconia (CZ) Stone?

Cubic Zirconia was first marketed in 1976, but was made as early as the mid 1920's in an attempt to produce a high temperature ceramic.  The original ceramics were white and opaque, but a new melt technique enabled more large transparent crystals.  Developed in 1973 in Moscow, the skull melting process uses a cold crucible to contain the melt within a crust of its own powder (the skull).  This technique is necessary because of the extremely high melting point of zirconium oxide (2750 degrees Celcius). 

CZ is one of the most common affordable substitutes for diamonds.  It can come in various colours and with the proper cleaning, it will retain its beauty for years.  It is a synthetic gemstone that is chemically composed of a cubic form of zirconium oxide (ZrO2) and a stabilizer (usually yttrium oxide or calcium oxide is added to obtain cubic conformation) + a colouring agent.  CZ has been made into at least 30 colours.  The cubic form of zirconium oxide can exist at room temperature only if it has the above mentioned stabilizer.  Natural cubic zirconia has only been found as inclusions in zircon (ZrSiO4), a naturally-occurring mineral .  Cubic Zirconia’s are cut in the same way diamonds are cut.  Depending on the styles, our CZ’s are both machine-cut and hand-cut. 

On the Mohs Scale of Hardness, cubic zirconia has a value of 8.25 to 8.5, while diamond has a hardness of 10.  Cubic zirconia has more dispersion and is more durable than glass making it a more popular simulant for diamond or other gemstones. 

Identification:

A thermal conductivity probe or an infra-red reflectometer provides the best separation from diamond for mounted stones.  The specific gravity (SG) for an unmounted stone is an adequate separation.  Diamond has an SG of 3.52, while CZ has an SG of 5.86, or 1.7 times that of diamond.  Earlier versions of CZ material often contained small almost dodecahedral (12-sided) inclusions. 

There may be polishing or wear scratches.  The girdle, which may be partially polished is often different from the regular grainy surface of a diamond girdle.  It may also show vertical polishing lines and sometimes has 2 planes.  CZ rarely has the lustre of a polished diamond girdle.  Earlier versions of CZ also flouresced orangish yellow under long wave UV light.