Zircon vs Opal
Zircon is harder (Mohs 6.5–7.5) 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.
Zircon has the higher refractive index (1.925–1.984 vs 1.450), which a refractometer (over-the-limit reading) can use to separate them.
Zircon is denser (SG 4.69 vs 2.15); a zircon of the same size weighs about 118% more.
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| Property | Zircon | Opal |
|---|---|---|
| Species / material | Zircon | Opal (hydrated silica) |
| Mohs hardness | 6.5–7.5 | 5.5–6.5 |
| Refractive index | 1.925–1.984 | 1.450 |
| Specific gravity | 4.69 | 2.15 |
| Crystal system | Tetragonal | Amorphous |
| Birefringence | 0.059 | None |
Values are typical ranges from standard gemmological references; individual stones can vary.