Tanzanite
Varietyof Zoisite
Tanzanite is the blue-violet gem variety of zoisite. As a variety of Zoisite, it shares that species' composition (Ca2Al3[Si2O7][SiO4]O(OH)), crystal structure, and hardness; the distinction is the appearance defined above.
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About Zoisite
Full reference data — crystallography, X-ray diffraction, and cited physical properties — is on the Zoisite species page.
| Formula | Ca2Al3[Si2O7][SiO4]O(OH) |
|---|---|
| Hardness (Mohs) | 6-6.5 |
| Specific gravity | 3.25-3.37 |
| Density (calculated) | 3.333 |
| Crystal system | orthorhombic |
| Color range | brown, gray, green, red, white, yellow |
| Luster | pearly, vitreous |
| Streak | red |