Cochise College          Photos of Minerals

                          Geology Home Page                

                          Roger Weller, geology instructor

                          wellerr@cochise.edu
                                  copyright 2007-R.Weller

 

Mineral Information on:
cordierite


Chemical Group:   silicate

Chemical Formula: 
Mg2Al4Si5O18

Color:  various shades of blue         Luster:  vitreous    

Transparency:  transparent to translucent                                                                    

 

Hardness:  7 to 7.5               Specific Gravity:  2.60 to 2.66                Fracture:

Cleavage:  (010) poor
 

Special Properties:  Cordierite is strongly pleochric (different colors in different directions).

 

Crystal Forms:  Orthorhombic system
     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.