What is cubic zirconia?
By Jared James · Last updated 21 May 2026
Definition
Cubic zirconia, shortened to CZ, is a synthetic gemstone made from zirconium dioxide, grown in a laboratory and cut to resemble a diamond. It is hard, usually colourless and catches the light convincingly, which is why it became the dominant diamond simulant when commercial production began in the 1970s. CZ is not the same as zircon, which is a natural mineral, and it is distinct from lab-grown diamond, which is genuine diamond. CZ costs a fraction of a diamond and can be made in a range of colours.
Frequently asked questions
- How can you tell cubic zirconia from a real diamond?
- A few practical checks help. CZ is heavier than diamond for the same size, slightly warmer to the touch initially, and shows more rainbow fire than most diamonds. A jeweller can test it immediately with a thermal or electrical conductivity tester, and under magnification CZ typically shows no inclusions, which real diamonds almost always do.
- Does cubic zirconia last as long as a diamond?
- It is reasonably hard but softer than diamond, rating about 8 to 8.5 on the Mohs scale compared with diamond's 10. It will scratch and cloud over years of daily wear, particularly in a ring, while a diamond holds its surface much longer. For occasional-wear pieces CZ stays bright for years.
- Is cubic zirconia the same as moissanite?
- No. Moissanite is silicon carbide, a different compound entirely, and it is closer to diamond in hardness and brilliance than CZ is. Moissanite is more durable and tends to hold its sparkle better over time, though CZ is significantly less expensive.
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