The confusion between cubic zirconia (CZ) and lab-created diamonds (LGDs) arises because both are synthetic alternatives to natural diamonds grown in a laboratory. However, they are fundamentally different materials with distinct chemical makeups and physical properties. Lab-created diamonds are genuine diamonds, sharing the exact structure of their earth-mined counterparts. Cubic zirconia, conversely, is classified only as a diamond simulant. Understanding the distinctions between these two materials is important for any consumer considering a jewelry purchase.
Fundamental Differences in Chemical Structure
The most significant difference lies in the atomic composition of the two stones. A lab-created diamond is pure crystallized carbon, represented by the chemical symbol C, arranged in an isometric crystal lattice structure. This makes its chemical and physical properties identical to a diamond formed deep within the Earth’s mantle. The only distinction is its origin, as LGDs are grown in controlled environments using processes like High-Pressure/High-Temperature (HPHT) or Chemical Vapor Deposition (CVD).
Cubic zirconia is not carbon-based at all, but rather a synthetic crystal composed of zirconium dioxide, or $\text{ZrO}_2$. This material is a diamond simulant, grown solely to imitate the appearance of a diamond without sharing its underlying chemistry. The production of CZ involves melting zirconium oxide powder with stabilizers like magnesium or calcium at extremely high temperatures, typically near 5,000°F.
The disparity in their chemical formulas means that CZ is a compound, while LGDs are elemental carbon, resulting in distinct reactions to heat and other tests. For example, a diamond is an excellent thermal conductor, a property that CZ lacks entirely. This difference in thermal conductivity is one of the quickest ways gemologists can differentiate the stones.
Comparing Physical Durability and Optical Performance
The variation in chemical structure translates directly into practical differences in durability, measured by hardness on the Mohs scale. Lab-created diamonds share the same maximum rating of 10 as natural diamonds, making them the hardest known material and extremely resistant to scratching and surface wear. This high degree of hardness ensures that a lab-created diamond will retain its polish and brilliance over a lifetime of daily wear.
Cubic zirconia ranks significantly lower on the Mohs scale, typically between 8 and 8.5. While this still indicates a hard material, the difference from 10 means CZ is much more susceptible to abrasion from common household dust, which can cause it to become cloudy over time. The lower hardness also makes CZ more prone to minor scratches and chipping, particularly along the facet edges.
The stones also interact with light differently due to their distinct optical properties. Diamond has a refractive index of approximately 2.42, producing a balanced mix of brilliance (white light reflection) and fire (colored light dispersion). Cubic zirconia has a lower refractive index (2.15 to 2.18) but a much higher dispersion rate. This high dispersion causes CZ to exhibit an excessive “rainbow effect” or fire, which can make the stone appear unnatural compared to a diamond’s sparkle.
CZ is also significantly denser than diamond. A CZ stone will weigh approximately 1.7 times more than an LGD of the same physical size, a difference noticeable when comparing stones of equal diameter.
Market Value and Consumer Cost
The differences in composition and properties lead to a disparity in their economic standing and cost for consumers. Cubic zirconia is a mass-produced item that requires less complex technology to manufacture than a lab-created diamond. Consequently, CZ has an extremely low cost, with virtually no intrinsic or resale value once purchased.
Lab-created diamonds, conversely, are formed through a complex, energy-intensive process that replicates the conditions of Earth’s mantle. Because they are chemically, physically, and optically identical to natural diamonds, LGDs are priced significantly higher than CZ, though they are often more affordable than their mined counterparts. LGDs follow the same grading standards as natural diamonds, retaining substantial intrinsic value and a much higher price point than CZ.