gemstone

Iolite

Cordierite (Magnesium Aluminum Silicate, (Mg,Fe)2Al3(AlSi5O18))

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

Hardness: 7 to 7
Luster: Vitreous

Identified August 2, 2026More gemstone →

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Physical properties

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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