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Cordierite color stone basic properties

Name Origin Corfierite is named after Mr. Cordier, a French geologist who first studied its crystals. Iolite is from Greek ios (violet) and lithos (stone)
Chemical Formula (Mg,Fe)2 Al4Si5O18
Color Blue, bluish violet, smoky blue; rarely greenish, gray, yellowish, brown
Hardness 7 - 7.5 on Mohs Scale
Crystal System Orthorhombic. Crystals prismatic with rectangular cross section; also massive, granular; may be pseudohexagonal. Note: Indialite is hexagonal.
Cleavage Distinct 1 direction. Fracture conchoidal. Brittle
Specific Gravity (SG) 2.53 - 2.78
Pleochroism Intense and distinctive
Mg-rich crystals: pale yellow to green/pale blue/violet, violet-blue
Luster vitreous
Stone sizes
 Iolites are frequently in the 1-10 carat range, dichroic with blue to violet color. Large cleen stones free of inclusions are not common at all, but gems over 30 carats have been reported
Occurrence In altered aluminous rocks; igneous rocks; alluvial gravels
Note: Cordierite is better known for its gem name which is iolite. This mineral is also called as water sapphire. Cordierite is magnesium aluminum silicate and crystallizes in orthorhombic system. The crystal structure of Cordierite has many similarities to that of beryl; indialite, the dimorph, in fact has the same structure as beryl. This is one of the minerals which shows distinct color changes or pleochroism, from a dark blue to a light blue to yellowish-white, when viewed from different directions. Cordierite as its gem form (iolite) is used widely in jewellery. In order to maximize the amount of color maybe revealed by the gem, the table facet must be cut at right angles to the prism faces. Iolite is however, not often faceted.  
Cordierite color stone
Cordierite color stone Colorado
Tremolite-Cordierite stone
Tremolite-Cordierite stone, Montauban Quebec Canada
Photo Credit: www.shutterstone.com