Opal vs Pearl
Opal is harder (Mohs 5.5–6.5) than Pearl (Mohs 2.5–4.5), so it resists scratching better; Pearl is softer than quartz dust (7) and needs more care in everyday rings.
Pearl has the higher refractive index (1.53–1.69 vs 1.450), which a refractometer can use to separate them.
Pearl is denser (SG 2.71 vs 2.15); a pearl of the same size weighs about 26% more.
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| Property | Opal | Pearl |
|---|---|---|
| Species / material | Opal (hydrated silica) | Organic (nacre) |
| Mohs hardness | 5.5–6.5 | 2.5–4.5 |
| Refractive index | 1.450 | 1.53–1.69 |
| Specific gravity | 2.15 | 2.71 |
| Crystal system | Amorphous | Organic |
| Birefringence | None | Not applicable |
Values are typical ranges from standard gemmological references; individual stones can vary.