metamorphic
Cordierite (Iolite) in Quartz
Cordierite (Magnesium iron aluminium cyclosilicate) - Mg2Al4Si5O18
Hardness: 7-7.5 on Mohs scale. Color: Blue, violet-blue, or grey-green (pleochroic). Luster: Vitreous to greasy. Crystal structure: Orthorhombic. Specific gravity: 2.58-2.66.
- Hardness
- 7-7
- Color
- Blue, violet-blue, or grey-green (pleochroic)
- Luster
- Vitreous to greasy
Identified More metamorphic →
Explore Cordierite (Iolite) in Quartz in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7-7.5 on Mohs scale. Color: Blue, violet-blue, or grey-green (pleochroic). Luster: Vitreous to greasy. Crystal structure: Orthorhombic. Specific gravity: 2.58-2.66.
Formation & geological history
Formed through the contact or regional metamorphism of argillaceous (clay-rich) rocks. Common in pelitic schists and gneisses, often associated with garnet and sillimanite.
Uses & applications
The gemstone variety (iolite) is used in jewelry. Industrial uses include thin-film substrates and high-temperature ceramics due to its low thermal expansion.
Geological facts
Iolite is also known as the "Viking Compass Stone" because its pleochroic properties allowed ancient navigators to determine the direction of the sun on overcast days by rotating a slice of the crystal.
Field identification & locations
Identified by its signature violet-blue color and strong pleochroism (changing color when viewed from different angles). Commonly found in Sri Lanka, Madagascar, Brazil, and India.
