Iolite
CordieriteJewelryWiki Editorial·2 sources·Reviewed 2026-08-04
A violet-blue stone often sold as an affordable alternative to sapphire or tanzanite. Its defining trick is pleochroism so strong it is visible without instruments: the same stone looks blue-violet from one direction and nearly colourless or yellowish from another, which is why cutting orientation matters more here than in almost any other gem.
Properties
| Property | Value | Authority |
|---|---|---|
| Mohs hardness | 7–7½ [1] | — |
| Specific gravity | 2.53–2.78 [1] | — |
| Chemical formula | (Mg,Fe2+)2Al4Si5O18 Read from the species entry, Cordierite. A variety shares its species’ formula. [2] | — |
| Crystal system | Orthorhombic [1] | — |
| Suitability for daily wear | Very good, per IGS — but see the caution. Hardness of 7–7½ is ample for a ring; the risk with iolite is cleavage rather than scratching. [1] | — |
| Care cautions | Iolite is not heat-sensitive, per IGS. The practical risk is a sharp knock rather than abrasion, so avoid ultrasonic cleaners and settings that leave an edge exposed. [1] | — |
Sources
- International Gem Society — gemstone articles — International Gem Society (IGS, gemstone information articles (gemsociety.org))
- Handbook of Mineralogy — Mineral Data Publishing / Mineralogical Society of America (Handbook of Mineralogy, Mineral Data Publishing)