Iolite is also known as cordierite. It is a violet-blue stone that is called water sapphire because of its similarity to sapphire after cutting. Iolite can be recognized by its strong pleochroism. That is visible without any equipment, which gives the gem its other name, dichroite. The best blue color is seen down the length of prismatic crystals. They may appear colorless when viewed across.
Occurrence
Gem-quality iolite is found in alluvial deposits as small, transparent, waterworn pebbles. These occur in Myanmar (Burma), Sri Lanka, India, and Madagascar. Other localities include Tanzania and Namibia. An iolite crystal is found in Finland, Norway, and Germany.
Iolite Properties
- Specific Gravity: 2.63
- Refractive Index: 1.53-1.55
- Birefringence (DR): 0.010
- Luster: Vitreous
- Crystal Structure: Orthorhombic
- Composition: Magnesium magnesium silicate
- Hardness: 7
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