gemstone
Iolite
Cordierite (Magnesium Aluminum Silicate, (Mg,Fe)2Al3(AlSi5O18))
AI-generated identification · may be incorrectHardness: 7 to 7.5 on the Mohs scale; Color: Blue to violet-blue, often showing strong pleochroism (appearing different colors from different angles); Luster: Vitreous; Crystal Structure: Orthorhombic; Cleavage: Poor; Specific Gravity: 2.53-2.78
- Hardness
- 7 to 7
- Luster
- Vitreous
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Physical properties
Hardness: 7 to 7.5 on the Mohs scale; Color: Blue to violet-blue, often showing strong pleochroism (appearing different colors from different angles); Luster: Vitreous; Crystal Structure: Orthorhombic; Cleavage: Poor; Specific Gravity: 2.53-2.78
Formation & geological history
Forms primarily in metamorphic rocks such as contact- or regionally-metamorphosed argillaceous rocks, and in igneous rocks like granitic pegmatites.
Uses & applications
Used primarily as a gemstone in jewelry, and historically used by ancient Viking navigators as a polarizing filter to locate the sun on cloudy days.
Geological facts
Iolite is also known as the 'water-liner' or Viking's Compass due to its intense pleochroism, which helps in determining the direction of polarized light.
Field identification & locations
Identified by its distinctive violet-blue color and strong trichroism. Commonly found in India, Sri Lanka, Madagascar, Brazil, and the United States.
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