Iolite
bluepurple · Cordierite family
| Also known as | Cordierite (Cordierite family) |
|---|---|
| Colour | Blue, Purple |
| Mohs hardness | 7–7.5 |
| Lustre | Greasy or vitreous |
| Streak | White |
| Crystal system | Orthorhombic |
| Transparency | Transparent to translucent |
| Cleavage | Fair on {100}, poor on {001} and {010} |
| Fracture | Subconchoidal |
| Specific gravity | 2.57–2.66 |
What is Iolite?
Cordierite (mineralogy) or iolite (gemology) is a magnesium iron aluminium cyclosilicate. Iron is almost always present, and a solid solution exists between Mg-rich cordierite and Fe-rich sekaninaite with a series formula: (Mg,Fe)2Al3(Si5AlO18) to (Fe,Mg)2Al3(Si5AlO18). A high-temperature polymorph exists, indialite, which is isostructural with beryl and has a random distribution of Al in the (Si,Al)6O18 rings. Cordierite is also synthesized and used in high temperature applications such as catalytic converters and pizza stones.
How to identify Iolite
- Lustre: Greasy or vitreous.
- Hardness: Mohs 7–7.5 — hard enough to scratch glass.
- Streak: White.
- Habit: Orthorhombic crystal system.
Iolite value
Iolite is a fine gemstone priced per carat by quality — colour, clarity, cut, carat and origin — not by weight in grams. Typical market ranges:
| Quality | Price per carat |
|---|---|
| Commercial | $10–$50 / ct |
| Good | $30–$200 / ct |
| Fine | $100–$800 / ct |
| Top | $200–$2,000 / ct |
Ranges cross-validated across two independent research passes against gemstone price guides, 2026-06 — sources: gia.edu, naturalgemstones.com. Colour saturation, clarity, cut and origin move the price enormously, and treatments or lab-grown stones sell for a fraction — so this is a guide, not an appraisal. Have anything valuable checked by a certified gemmologist. See the full crystal & gemstone value guide.
