Geology Home Page
Roger Weller, geology instructor
Chemical Group: silicate
Chemical Formula: Mg2Al4Si5O18
Color: various shades of blue Luster: vitreous
Transparency: transparent to translucent
Hardness: 7 to
Specific Gravity: 2.60 to 2.66
Cleavage: (010) poor
Special Properties: Cordierite is strongly pleochric (different colors in different directions).
Crystals are usually short prismatic, pseudohexagonal twins.
Mineral Associations: Cordierite is found in granites and gneiss
Identifying Characteristics: resembles quartz; blue color helps to distinguish iolite.
Uses: as a gemstone (water sapphire or saphir d'eau)
Occurrences: Bavaria, Finland, Greenland, Madagascar, Ceylon:
in the USA from Connecticut.
Toxicity: when-swallowed- when inhaled-
Additional Information: Cordierite is also known as Iolite or Dichroite.