Ruby vs Opal
Ruby is harder (Mohs 9) 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.
Ruby has the higher refractive index (1.762–1.770 vs 1.450), which a refractometer can use to separate them.
Ruby is denser (SG 4 vs 2.15); a ruby of the same size weighs about 86% more.
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| Property | Ruby | Opal |
|---|---|---|
| Species / material | Corundum | Opal (hydrated silica) |
| Mohs hardness | 9 | 5.5–6.5 |
| Refractive index | 1.762–1.770 | 1.450 |
| Specific gravity | 4 | 2.15 |
| Crystal system | Trigonal | Amorphous |
| Birefringence | 0.008–0.010 | None |
Values are typical ranges from standard gemmological references; individual stones can vary.