Cordierite Archives - Cochise College Geology

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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

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.

Additional Information: Cordierite is also known as Iolite or Dichroite.

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