Cubic Zirconia (CZ) is a synthetic, crystalline material composed of zirconium dioxide (ZrO2). It is a widely used and affordable diamond simulant in the jewelry industry, valued for its clarity and brilliance. Hardness is one of the most important physical properties to consider when assessing a gemstone’s suitability for jewelry. This characteristic determines its resistance to scratching and overall wearability, which is central to predicting its durability.
Understanding Hardness Measurement
The Mohs Scale of Mineral Hardness is used to determine a material’s resistance to scratching or abrasion. This is an ordinal scale of ten common minerals, where a material with a higher number can visibly scratch any material with a lower number. The scale begins with talc at 1 and ends with the hardest natural material, diamond, at 10. For example, quartz, a major component of household dust, has a Mohs hardness of 7.
The Hardness Value of Cubic Zirconia
Cubic Zirconia consistently rates between 8.0 and 8.5 on the Mohs scale of hardness, depending on its specific manufacturing formula. This rating places it among the harder synthetic gemstones, just below ruby and sapphire (Mohs 9). The high hardness of CZ results from its robust, tightly packed cubic crystal structure, engineered during synthesis. This 8.0 to 8.5 hardness means CZ is highly resistant to scratching from many common materials, including abrasive quartz dust (Mohs 7). However, CZ can be scratched by other CZ stones or by harder materials like moissanite, corundum, or diamond.
Distinguishing CZ from Diamond
The hardness difference between Cubic Zirconia (8.0–8.5) and diamond (10) is a major distinction with significant implications for longevity and wear. Diamond is the hardest known substance, and the difference between a 9 (corundum) and a 10 (diamond) on the Mohs scale represents a vast increase in absolute hardness. This superior hardness makes diamond virtually impervious to scratching in daily use, while CZ is more susceptible to surface abrasion and dulling over a long period of time. Beyond hardness, CZ and diamond can be separated by several other physical properties.
Other Physical Properties
Cubic Zirconia is significantly denser, weighing about 1.7 times more than a diamond of the same size. CZ exhibits a higher dispersion, which is the ability to split white light into spectral colors, resulting in an excessive “rainbow-like” flash, often referred to as “fire.” CZ also lacks the thermal conductivity of diamond, a property that professional gem testers use to instantly differentiate the two materials.