Ruby vs Spinel
Ruby is harder (Mohs 9) than Spinel (Mohs 8), so it resists scratching better.
Ruby has the higher refractive index (1.762–1.770 vs 1.718), which a refractometer can use to separate them.
Ruby is denser (SG 4 vs 3.6); a ruby of the same size weighs about 11% more.
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| Property | Ruby | Spinel |
|---|---|---|
| Species / material | Corundum | Spinel |
| Mohs hardness | 9 | 8 |
| Refractive index | 1.762–1.770 | 1.718 |
| Specific gravity | 4 | 3.6 |
| Crystal system | Trigonal | Cubic |
| Birefringence | 0.008–0.010 | None (isotropic) |
Values are typical ranges from standard gemmological references; individual stones can vary.