Opal vs Cubic zirconia
Cubic zirconia is harder (Mohs 8–8.5) than Opal (Mohs 5.5–6.5), so it resists scratching better; Opal is softer than quartz dust (7) and needs more care in everyday rings.
Cubic zirconia has the higher refractive index (2.15–2.18 vs 1.450), which a refractometer (over-the-limit reading) can use to separate them.
Cubic zirconia is denser (SG 5.8 vs 2.15); a cubic zirconia of the same size weighs about 170% more.
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| Property | Opal | Cubic zirconia |
|---|---|---|
| Species / material | Opal (hydrated silica) | Synthetic zirconium oxide |
| Mohs hardness | 5.5–6.5 | 8–8.5 |
| Refractive index | 1.450 | 2.15–2.18 |
| Specific gravity | 2.15 | 5.8 |
| Crystal system | Amorphous | Cubic |
| Birefringence | None | None (isotropic) |
Values are typical ranges from standard gemmological references; individual stones can vary.
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