Iolite
From The Gemology Project
Iolite | |
---|---|
Chemical composition | Complex Mg-Al (magnesium aluminum) silicate |
Crystal system | Orthorhombic |
Habit | Massive, prisms |
Cleavage | Distinct, basal |
Fracture | Sub-conchoidal |
Hardness | 7.5 |
Optic nature | Biaxial - |
Refractive index | 1.53 - 1.55 |
Birefringence | 0.008 - 0.012 |
Dispersion | Low, 0.017 |
Specific gravity | 2.58 - 2.74 |
Lustre | Vitreous |
Pleochroism | Strongly trichroic |
Iolite is also named "water sapphire", cordierite or dichroite. Iolite has been worn for centuries and derives its name from “Ios” - the Greek word for violet. Due to it’s strong pleochroism, ancient Vikings used iolite for navigation on cloudy days. The gemstone acted as a polarizing filter and allowed the ancient sailors to determine the position of the sun. The soft blue color makes it a very attractive gemstone. Iolite is the 21st anniversary gemstone.