Emerald vs Opal
Emerald is harder (Mohs 7.5–8) 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.
Emerald has the higher refractive index (1.577–1.583 vs 1.450), which a refractometer can use to separate them.
Emerald is denser (SG 2.72 vs 2.15); a emerald of the same size weighs about 27% more.
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| Property | Emerald | Opal |
|---|---|---|
| Species / material | Beryl | Opal (hydrated silica) |
| Mohs hardness | 7.5–8 | 5.5–6.5 |
| Refractive index | 1.577–1.583 | 1.450 |
| Specific gravity | 2.72 | 2.15 |
| Crystal system | Hexagonal | Amorphous |
| Birefringence | 0.005–0.009 | None |
Values are typical ranges from standard gemmological references; individual stones can vary.