RocksdayIolite vs Sapphire
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
Gem corundum of any color except red. Blue sapphire gets its color from iron and titanium.
Photo: James St. John, CC BY 2.0
Quick tests
- Hardness: Sapphire is clearly harder: Mohs 9 versus 7–7.5.
- Heft: Sapphire feels noticeably heavier for its size (specific gravity 3.95–4.03 vs 2.57–2.66).
Key differences
- Sapphire is much harder and heavier.
- Iolite is much softer and changes from blue to almost clear as you rotate it.
Side by side
| Property | Iolite | Sapphire |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 7–7.5 | 9 |
| Luster | Vitreous | Adamantine to vitreous |
| Streak | White | White |
| Colors | Blue, Purple, Gray | Blue, Yellow, Pink, Orange |
| Crystal system | Orthorhombic | Trigonal |
| Specific gravity | 2.57–2.66 | 3.95–4.03 |
| Formula | (Mg,Fe)₂Al₄Si₅O₁₈ | Al₂O₃ |
| Found in | India; Sri Lanka | Sri Lanka; Madagascar |
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 sapphire
- Hardness 9 — only diamond scratches it.
- Barrel or tapered six-sided crystals.
- Heavy for its size.
Crystal system: Trigonal
Full Sapphire guide →More comparisons
Could you tell them apart from a blurry close-up?
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