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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.