Peridot vs Opal
Peridot is harder (Mohs 6.5–7) 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.
Peridot has the higher refractive index (1.654–1.690 vs 1.450), which a refractometer can use to separate them.
Peridot is denser (SG 3.34 vs 2.15); a peridot of the same size weighs about 55% more.
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| Property | Peridot | Opal |
|---|---|---|
| Species / material | Olivine (forsterite) | Opal (hydrated silica) |
| Mohs hardness | 6.5–7 | 5.5–6.5 |
| Refractive index | 1.654–1.690 | 1.450 |
| Specific gravity | 3.34 | 2.15 |
| Crystal system | Orthorhombic | Amorphous |
| Birefringence | 0.035–0.038 | None |
Values are typical ranges from standard gemmological references; individual stones can vary.