Cordierite-group minerals (CGM): cordierite, Mg2[Al4Si5O18], and sekaninaite, Fe2[Al4Si5O18], form a solid solution defined by the VI(Mg↔Fe2+) substitution. They are characteristic components in aluminous metamorphic and magmatic rocks including some granites and granitic pegmatites. They are framework silicates with six-membered rings of corner-sharing T2 tetrahedra linked by additional T1 tetrahedra, the octahedral M-sites and channel sites (Ch). Typically, the natural samples contain minor Mn, Be, Li, and Zn as well as channel cations and volatiles. The general...

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