Cubic zirconia, CZ for short, is a lab-made crystal of zirconium dioxide (ZrO₂). It is colourless, bright and very consistent, which makes it well suited to the small accent stones in a halo, a pavé band or the shoulders of a ring. In our rings, the accent stones are CZ unless the product says otherwise.
What it is
Zirconium dioxide is a hard, heat-resistant oxide. At room temperature its stable crystal form is not cubic; adding a stabiliser, usually yttrium oxide, locks it in the cubic form, which is the one that is clear and sparkling.
Cubic zirconia is not zircon. Zircon is a different, natural gemstone (zirconium silicate) with a similar name.
How it is made
CZ is grown by a method called skull melting, developed at the Lebedev Physical Institute in Moscow in the early 1970s and in commercial production since 1976:
- Zirconium dioxide powder mixed with the stabiliser fills a water-cooled copper crucible.
- Radio-frequency induction heats the powder from within, until the centre melts at about 2,750 °C.
- The outer layer, kept cool by the copper, stays solid and becomes the container, or “skull”, for the melt.
- As the melt cools slowly, column-shaped crystals grow from the bottom up. They are then sawn and cut into gems.
Its properties
| Property | Cubic zirconia |
|---|---|
| Composition | zirconium dioxide, ZrO₂ (stabilised) |
| Hardness (Mohs) | 8 to 8.5 |
| Refractive index | 2.15 to 2.18 |
| Dispersion (fire) | 0.058 to 0.066 |
| Density | 5.6 to 6.0 g/cm³ |
| Optical character | singly refractive |
CZ is dense: a stone the size of a diamond weighs roughly 1.6 to 1.7 times as much. Its fire is stronger than diamond’s and its brilliance a little lower than diamond’s and moissanite’s.
Why it suits small accent stones
- At one or two millimetres, what matters is a clean, colourless sparkle, and CZ delivers it consistently from stone to stone.
- It can be cut precisely and matched closely in colour and size, so a row of pavé or a halo looks even.
- It keeps the cost of dozens of tiny stones reasonable, so the budget goes into the centre stone and the metalwork.
Its limits
CZ is softer than moissanite (9.25) and diamond (10). Over years of daily wear, the edges of its facets can wear slightly, and its surface can look dull when skin oils and lotion build up. Regular gentle cleaning keeps it bright, and a jeweller can replace a worn accent stone.
How we name it
We always call it cubic zirconia, or CZ, and never a diamond. In French it is « oxyde de zirconium ».
Care
Warm water, a little mild soap and a soft brush; rinse and dry. Keep it away from harsh household chemicals, and take your ring off for gardening, the gym or heavy work.