In legends, ancient Viking navigators used thin slices of iolite as filters to help locate the sun on cloudy days. Whether or not the tales are true, iolite (mineralogists call it cordierite) can be fashioned into beautiful gems. Strongly pleochroic iolite has been incorrectly called “water sapphire,” as it can display a blue to violet hue in one direction and pale yellow to colorless in another.
Ios
Iolite’s name is from the Greek word ios, meaning violet.
Pleochroic
When you turn iolite, you’ll see three distinct colors in three crystal directions.
Au Natural
Iolite is not typically treated. This is an attractive selling point for some consumers.
Facts
- Mineral: Iolite (Cordierite)
- Chemical composition: Mg2Al4Si5O18
- Color: Violetish blue (pleochroic colorless-yellow)
- Refractive index: 1.542 – 1.551
- Birefringence: +0.045, -0.011
- Specific gravity: 2.61
- Mohs hardness: 7.0 – 7.5