Ruby vs Alexandrite
Ruby is harder (Mohs 9) than Alexandrite (Mohs 8.5), so it resists scratching better.
Their refractive indices are close (1.762–1.770 vs 1.746–1.755), so combine RI with SG, optic character, or inclusions to separate them.
Ruby is denser (SG 4 vs 3.73); a ruby of the same size weighs about 7% more.
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| Property | Ruby | Alexandrite |
|---|---|---|
| Species / material | Corundum | Chrysoberyl |
| Mohs hardness | 9 | 8.5 |
| Refractive index | 1.762–1.770 | 1.746–1.755 |
| Specific gravity | 4 | 3.73 |
| Crystal system | Trigonal | Orthorhombic |
| Birefringence | 0.008–0.010 | 0.008–0.010 |
Values are typical ranges from standard gemmological references; individual stones can vary.