Amethyst vs Tanzanite
Amethyst is harder (Mohs 7) than Tanzanite (Mohs 6–7), so it resists scratching better; Tanzanite is softer than quartz dust (7) and needs more care in everyday rings.
Tanzanite has the higher refractive index (1.691–1.700 vs 1.544–1.553), which a refractometer can use to separate them.
Tanzanite is denser (SG 3.35 vs 2.65); a tanzanite of the same size weighs about 26% more.
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| Property | Amethyst | Tanzanite |
|---|---|---|
| Species / material | Quartz | Zoisite |
| Mohs hardness | 7 | 6–7 |
| Refractive index | 1.544–1.553 | 1.691–1.700 |
| Specific gravity | 2.65 | 3.35 |
| Crystal system | Trigonal | Orthorhombic |
| Birefringence | 0.009 | 0.008–0.013 |
Values are typical ranges from standard gemmological references; individual stones can vary.
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