The affordability and visual similarity of Cubic Zirconia (CZ) to natural diamonds have made it a widely popular substitute in jewelry. While CZ is created entirely by human technology in a controlled setting, its chemical makeup is fundamentally different from a diamond. Clarifying the manufacturing process and proper gemological classification provides a clearer understanding of what CZ is and how it compares to its natural counterpart.
Defining Synthetic Gems and Simulants
Gemstones are classified into distinct categories based on their origin and chemical composition. Natural gems form in the earth without human intervention, possessing unique chemical and structural properties.
The term “synthetic gem” refers to a material grown in a laboratory that shares the exact same chemical composition and crystal structure as its natural equivalent. For example, a lab-grown diamond is a synthetic diamond because it is pure carbon arranged in a cubic lattice, just like a mined diamond. The only difference is the origin.
Cubic Zirconia is not a synthetic diamond; instead, it is classified as a simulant. A simulant is a material that imitates the appearance of a more expensive gem but has a completely different chemical structure. CZ serves as a diamond simulant, sharing visual characteristics like sparkle but possessing a unique chemical identity.
The Creation Process of Cubic Zirconia
Cubic Zirconia is a crystalline form of Zirconium Dioxide (\(\text{ZrO}_2\)), a compound that does not form naturally in the cubic crystal structure. The entire manufacturing process takes place in a highly controlled environment, making it a fully synthesized product. This process is necessary because Zirconium Dioxide has an extremely high melting point, around 2,750 degrees Celsius.
Manufacturers use a specialized technique known as the Skull Melt method due to this intense heat requirement. Traditional crucibles would melt at such temperatures. The Skull Melt method solves this challenge by using the Zirconium Dioxide powder itself to form the container.
The process involves placing the raw Zirconium Dioxide powder inside a water-cooled copper chamber. Radio-frequency (RF) induction heating is applied, which melts the material in the center while the outer layer remains solid, forming a self-containing “skull.” This solid shell prevents the molten core from touching and destroying the chamber walls.
To ensure the crystal grows in the desired cubic form, a stabilizing agent, typically Yttrium Oxide (\(\text{Y}_2\text{O}_3\)), is added to the melt. Once the material is fully melted, the RF power is slowly reduced, allowing the molten core to cool and crystallize over several hours. This controlled cooling yields large, flawless single crystals of Cubic Zirconia.
Key Differences Between CZ and Natural Diamonds
Cubic Zirconia and natural diamonds are easily distinguished based on several physical and optical properties that impact their wearability and appearance. The most significant difference is durability, measured on the Mohs scale of hardness. A natural diamond rates a perfect 10, while CZ ranks lower at 8 to 8.5. This difference means CZ is more susceptible to scratching and shows wear faster than a diamond over time.
CZ also handles light differently, which is noticeable in its sparkle. A diamond has a Refractive Index (RI) of 2.42, which measures how much light is bent as it passes through the stone, creating its signature brilliance. Cubic Zirconia has a lower RI, typically ranging from 2.15 to 2.18, meaning it bends light less sharply and can appear less brilliant.
CZ exhibits a higher dispersion value, which is the property that splits white light into the colors of the rainbow, often called “fire.” A diamond’s dispersion is 0.044, while CZ’s is higher, ranging from 0.058 to 0.066. This higher dispersion creates an excessive rainbow effect that often gives CZ an unnatural flash of color compared to the more subtle fire of a diamond.
Finally, the two materials have a stark contrast in density. Cubic Zirconia is substantially heavier than diamond, with a density between 5.5 and 6.0 \(\text{g}/\text{cm}^3\), compared to a diamond’s 3.5 to 3.53 \(\text{g}/\text{cm}^3\). This means a CZ stone of the same size will weigh about 1.7 times more, a difference often noticeable when holding the stones. These physical differences ultimately contribute to the vast cost differential, with CZ being a small fraction of the price of a natural diamond.