Cubic Zirconia (CZ) is a synthetic material, a man-made compound of zirconium dioxide, used extensively as a diamond simulant in jewelry. It is colorless and possesses a remarkable brilliance that closely mimics a genuine gemstone. Glass, a common material composed primarily of silica, is often encountered in everyday settings, from windows to drinking vessels. A frequent question arises regarding whether this popular diamond simulant can leave a permanent mark on the much softer glass surface.
The Definitive Answer
The answer to whether Cubic Zirconia can scratch glass is unequivocally yes. This is a predictable outcome determined by the inherent physical properties of each material. A CZ crystal, when dragged across a common glass surface with sufficient pressure, will produce a visible, permanent scratch. The ability of one substance to abrade another is a fundamental concept in material science, governed by the difference in their resistance to surface deformation.
Understanding the Mohs Hardness Scale
The principle that governs this scratching is quantified using the Mohs Hardness Scale. This qualitative ordinal scale ranks materials from 1 (softest) to 10 (hardest) based on their resistance to being scratched by another material. Friedrich Mohs developed this system in 1812. A material with a higher Mohs rating can invariably scratch any material with a lower rating.
Cubic Zirconia is a relatively hard material, ranking between 8 and 8.5 on the Mohs scale. This high value places it among the harder gemstones used in jewelry. Common soda-lime glass, used in most windows and bottles, registers much lower at approximately 5.5. Since CZ’s hardness is significantly greater than glass’s, the CZ crystal easily overcomes the bonds holding the glass surface together, leaving a permanent groove.
Why Scratching Glass Does Not Prove It Is a Diamond
The ability of Cubic Zirconia to scratch glass is often mistaken as a positive test for a genuine diamond. This assumption is flawed because while CZ is harder than glass, a diamond is harder than both, scoring a perfect 10 on the Mohs scale. Any diamond simulant scoring above 5.5, including CZ, will pass the glass scratch test, making the test inconclusive for diamond identification.
Distinguishing CZ from a true diamond requires examining other physical and optical properties. CZ has a lower refractive index, typically ranging from 2.15 to 2.18, compared to a diamond’s index of 2.42. CZ also exhibits a higher dispersion, or “fire,” which is the tendency to split white light into a pronounced rainbow of colors. This enhanced fire can sometimes appear unnaturally vibrant compared to a diamond’s more controlled brilliance.
Diamond possesses superior thermal conductivity, dissipating heat instantly, which is the basis for professional testing equipment. CZ is a thermal insulator and retains heat, causing it to fail a thermal probe test. CZ is also denser than diamond, being about 1.7 times heavier than a diamond of the same size. These distinct characteristics are far more reliable than the simple glass scratch test for accurate identification.