Cubic zirconia (CZ)

Cubic zirconia, usually abbreviated CZ, is a manmade gemstone material based on zirconium oxide. It is used as a diamond simulant in rings, earrings and pendants, among other jewellery. It can be colourless or produced in a range of colours.

Important distinctions

CZ is neither natural zircon, a separate mineral, nor laboratory-grown diamond. Its Mohs hardness is about 8.5, and it scratches more readily than diamond. The similar names zircon and zirconia do not establish material identity.

Buying and assessment

Ask for the stone and the metal to be described separately. A gold or silver hallmark does not identify the stone in a piece of jewellery. Have an unknown stone examined before calling it CZ or diamond. Record scratches, damaged facet edges and the condition of the setting as well.

Sources: GIA, Simulants or imitation gem materials; GIA, Zircon; GIA, What Are Simulated Diamonds?.