mineral

Iolite

Cordierite (Magnesium iron aluminium silicate)

AI-generated identification · may be incorrect

Hardness: 7-7.5 on Mohs scale; Color: Blue, violet-blue, smoky blue; Luster: Vitreous; Crystal Structure: Orthorhombic; Cleavage: Good in one direction; Specific Gravity: 2.58-2.66

Hardness: 7-7
Color: Blue, violet-blue, smoky blue
Luster: Vitreous

Identified June 26, 2026More mineral →

Explore Iolite in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 7-7.5 on Mohs scale; Color: Blue, violet-blue, smoky blue; Luster: Vitreous; Crystal Structure: Orthorhombic; Cleavage: Good in one direction; Specific Gravity: 2.58-2.66

Formation & geological history

Formed through the regional or contact metamorphism of aluminous rocks. Commonly found in schists, gneisses, and certain types of contact metamorphic zones. Formed throughout geological time where tectonic pressures are present.

Uses & applications

Primarily used as a gemstone in jewelry, especially as a more affordable substitute for sapphire. Also used in industrial ceramics and catalyst supports because of its low thermal expansion.

Geological facts

Known as the "Viking's Compass" because it was allegedly used by Viking navigators to find the sun on cloudy days due to its extreme pleochroism—it changes color from blue to yellowish-gray when viewed from different angles.

Field identification & locations

Identify in the field by its distinct pleochroism (appearing different colors from different directions) and its tendency to look like a watery sapphire. Common locations include Sri Lanka, Myanmar, India, and Tanzania.