Iolite
Real mineral · uncommon · Mg₂Al₄Si₅O₁₈
The gem variety of cordierite, displaying extreme trichroism: blue, yellow, and near-colourless from three different directions. Viking navigators may have used thin slices as polarising filters to locate the sun in overcast conditions.
Identity
- Formula
- Mg₂Al₄Si₅O₁₈
- Chemical class
- silicate
- Also known as
- Cordierite, Water sapphire (archaic), Viking compass stone
Crystallography
- Crystal system
- orthorhombic
- Habits
- massive, prismatic
- Fracture
- subconchoidal
Physical properties
- Mohs hardness
- 7.5
- Density
- 2.61 g/cm³
- Luster
- vitreous
- Colors
- blue, violet, gray, yellow
- Streak
- white
- Transparency
- transparent, translucent
Geology
- Origins
- metamorphic
- Host rocks
- schist, gneiss, granite
- Associated minerals
- Garnet, Kyanite, Sillimanite, Quartz
- Geography
- India, Sri Lanka, Mozambique, Brazil, Finland
Classification
- Rarity
- uncommon
- Gem quality
- Yes
Arcane properties
- Affinity
- water, air
- Effects
- scrying
- Planar origin
- Material Plane
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