Iolite

Iolite Chemical Composition:
Cordierite (mineralogy) or iolite (gemology) is a magnesium iron aluminium cyclosilicate. Iron is almost always present and a solid solution exists between Mg-rich cordierite and Fe-rich sekaninaite with a series formula: (Mg,Fe) 2Al 3(Si 5AlO 18) to (Fe,Mg) 2Al 3(Si 5AlO 18).
Dana classification: 61.02.01.01; Cordierite gr...
Pleochroism: X = pale yellow, green; Y = violet, ...
Crystal class: Dipyramidal (mmm); H-M symbol: ...
Mohs scale hardness: 7 - 7.5