Cubic Zirconia (CZ) is one of the most widely recognized materials used today as a diamond simulant. This highly brilliant stone is definitively lab-created, as virtually all gem-quality CZ is synthetic. It is manufactured specifically to mimic the visual characteristics of a diamond, providing a brilliant, colorless alternative at a fraction of the cost. Its man-made origin allows for consistent quality and mass production for widespread use in jewelry.
Composition and Synthetic Origin
Cubic zirconia is a crystalline form of zirconium dioxide. While zirconium dioxide exists naturally as the mineral baddeleyite, this natural form has a monoclinic crystal structure unsuitable for use as a gemstone. The cubic structure required for the stone’s characteristic appearance and brilliance is unstable at standard temperatures and pressures. Therefore, the material must be stabilized and grown in a laboratory setting to maintain the cubic structure, classifying it as a synthetic material. CZ is considered a simulant because it looks like a diamond but has a different chemical composition, unlike a synthetic diamond, which is chemically identical to a natural one.
The Skull Melt Manufacturing Process
The creation of gem-quality cubic zirconia requires a specialized industrial process known as the skull melt technique. This method is necessary because zirconium dioxide has an extremely high melting point, which is too high for any standard crucible material. The skull melt apparatus solves this problem by using the raw material to contain itself.
The process involves placing zirconium oxide powder, mixed with a stabilizing agent such as yttrium oxide, into a water-cooled copper container called the “skull.” Radio frequency (RF) induction heating melts the core of the powder. The intense cooling from the copper container keeps the outer layer of the powder solid, forming a self-contained shell that holds the molten interior. Once melted, the temperature is carefully reduced to allow the cubic crystals to grow. The resulting crystals, known as a boule, are then removed, sectioned, and prepared for cutting and polishing into gemstones.
How Cubic Zirconia Differs from Diamond
Despite its visual similarity, cubic zirconia differs from diamond across several measurable physical and optical properties.
Hardness
One of the most common ways to distinguish them is by measuring hardness. CZ scores 8 to 8.5 on the Mohs scale, while diamond scores the maximum 10. This difference means CZ is more susceptible to scratching and can lose its polish over time, especially with daily wear.
Density
Another significant difference is density, or specific gravity, as CZ is substantially heavier than diamond. A cubic zirconia stone will weigh about 1.7 times more than a diamond of the exact same size and cut. This disparity is often noticeable when comparing the weight of two stones of similar carat size.
Dispersion (Fire)
Cubic zirconia also exhibits a higher measure of light dispersion, which is the ability to split white light into spectral colors, often called “fire.” While this makes CZ produce more colorful flashes, the effect can appear too intense. This sometimes gives the stone an unnatural, “rainbow” appearance compared to the more balanced brilliance of a diamond.
Thermal Conductivity
Finally, diamond is an excellent thermal conductor, which is the basis for common diamond testing equipment. In contrast, cubic zirconia is a thermal insulator.