RocksdayIolite vs Tanzanite
How to tell them apart
Gem cordierite, a violet-blue stone that changes color dramatically depending on viewing direction.
Photo: Robert M. Lavinsky, CC BY-SA 3.0
Blue-violet zoisite found in only one small area of Tanzania. It shows different colors from different directions.
Photo: Didier Descouens, CC BY 3.0
Key differences
- Tanzanite is softer and heavier.
- Iolite is lighter and its colors shift from blue to near clear.
Side by side
| Property | Iolite | Tanzanite |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 7–7.5 | 6–7 |
| Luster | Vitreous | Vitreous |
| Streak | White | White |
| Colors | Blue, Purple, Gray | Blue, Purple |
| Crystal system | Orthorhombic | Orthorhombic |
| Specific gravity | 2.57–2.66 | 3.35 |
| Formula | (Mg,Fe)₂Al₄Si₅O₁₈ | Ca₂Al₃(SiO₄)(Si₂O₇)O(OH) |
| Found in | India; Sri Lanka | Merelani Hills, Tanzania |
Properties that are the same for both are grayed out.
How to identify iolite
- Violet-blue from one side, pale yellow-gray or clear from another.
- Hardness 7–7.5.
- Light for a blue gem.
Crystal system: Orthorhombic
Full Iolite guide →How to identify tanzanite
- Blue to violet, shifting color as you rotate it.
- Hardness about 6.5 — softer than sapphire.
- Most rough is brownish until heated.
Crystal system: Orthorhombic
Full Tanzanite guide →More comparisons
Could you tell them apart from a blurry close-up?
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