Cubic Zirconia Jewelry & Rings

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.

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. 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. It is in the isometric crystal system with a 4/mbar32/m crystal class and a Fm3m space group. 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. Since CZ is transparent, it is often faceted. It can be made in nearly any color and can be faceted into many cuts.

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. Though these compounds are both opaque, white ores, they melt together to form an amazing clear crystal.

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. This requires such high heat that a special radio frequency "skull crucible" must be used to melt the zirconia powder.

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.