Alexandrite vs Tanzanite
Alexandrite is harder (Mohs 8.5) than Tanzanite (Mohs 6–7), so it resists scratching better; Tanzanite is softer than quartz dust (7) and needs more care in everyday rings.
Alexandrite has the higher refractive index (1.746–1.755 vs 1.691–1.700), which a refractometer can use to separate them.
Alexandrite is denser (SG 3.73 vs 3.35); a alexandrite of the same size weighs about 11% more.
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| Property | Alexandrite | Tanzanite |
|---|---|---|
| Species / material | Chrysoberyl | Zoisite |
| Mohs hardness | 8.5 | 6–7 |
| Refractive index | 1.746–1.755 | 1.691–1.700 |
| Specific gravity | 3.73 | 3.35 |
| Crystal system | Orthorhombic | Orthorhombic |
| Birefringence | 0.008–0.010 | 0.008–0.013 |
Values are typical ranges from standard gemmological references; individual stones can vary.
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