Cubic zirconia (CZ) is a popular manufactured stone often used as a diamond substitute. The question of whether CZ jewelry can scratch surfaces like glass tables or window panes requires understanding a fundamental concept in materials science: hardness. Hardness dictates how resistant a material is to scratching or abrasion by another substance.
The Principle of Hardness
Material hardness measures a substance’s ability to resist scratching. Scientists quantify this characteristic using the Mohs scale of mineral hardness, developed by German mineralogist Friedrich Mohs in 1812. The scale is relative, ranking ten minerals from 1 (softest, like talc) to 10 (hardest, like diamond).
The rule is simple: a material can only scratch another if it ranks higher on the Mohs scale. For instance, quartz (Mohs 7) can scratch feldspar (Mohs 6) but cannot scratch topaz (Mohs 8). This principle determines whether cubic zirconia can mark glass.
Defining Cubic Zirconia and Glass Hardness
Cubic Zirconia is a synthetic crystalline substance made of zirconium dioxide. Prized for its diamond-like appearance, CZ is relatively hard, typically ranking between 8.0 and 8.5 on the Mohs scale. This places it above most common household materials.
In contrast, common glass, such as the soda-lime glass found in most windows and tabletops, is significantly softer. Standard glass usually registers a Mohs hardness value between 5.5 and 6.5. This range makes glass susceptible to scratching from many materials, including common sand (primarily quartz).
The Direct Answer: Can CZ Scratch Glass?
Based on the principle of relative hardness, the definitive answer is yes, cubic zirconia can easily scratch common glass. CZ (Mohs 8.0 to 8.5) is substantially harder than standard glass (Mohs 5.5 to 6.5). A harder material will always scratch a softer one when brought into contact under pressure.
This is important for practical reasons, especially regarding jewelry care and storage. CZ jewelry should not be stored loose with glass items, as the stone can abrade the surface. The ability of CZ to scratch glass is sometimes used in a “scratch test” to identify diamonds. However, while CZ scratches glass, it is much softer than a true diamond, which has a Mohs hardness of 10. CZ’s ability to mark glass confirms its hardness relative to glass, not its identity as a diamond.