Cordierite
Iolite
The 'Viking compass' - strongly pleochroic blue.
- Mohs hardness
- 7–7.5
- Crystal system
- Orthorhombic
- Composition
- Mg₂Al₄Si₅O₁₈
- Colours
- Violet-blue, Blue, Yellowish grey
- Origins
- Sri Lanka, India, Tanzania
Iolite (gem cordierite) shows three distinct colours from different crystal directions - blue, colourless and yellowish - making cutting orientation critical. Norse navigators reportedly used thin slices to locate the sun through cloud cover by polarisation.
A durable, affordable alternative to blue sapphire and tanzanite.
Treatments
What to know
- Generally untreated
Care & handling
How to wear it
- Durable for daily wear
- Ultrasonic generally safe
Jewellery use
Setting the gemstone
Excellent everyday gemstone - rings, pendants, earrings.