Ruby vs Amethyst
Ruby is harder (Mohs 9) than Amethyst (Mohs 7), so it resists scratching better.
Ruby has the higher refractive index (1.762–1.770 vs 1.544–1.553), which a refractometer can use to separate them.
Ruby is denser (SG 4 vs 2.65); a ruby of the same size weighs about 51% more.
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| Property | Ruby | Amethyst |
|---|---|---|
| Species / material | Corundum | Quartz |
| Mohs hardness | 9 | 7 |
| Refractive index | 1.762–1.770 | 1.544–1.553 |
| Specific gravity | 4 | 2.65 |
| Crystal system | Trigonal | Trigonal |
| Birefringence | 0.008–0.010 | 0.009 |
Values are typical ranges from standard gemmological references; individual stones can vary.