Gedrite
Gedrite is a crystal belonging to the orthorhombic ferromagnesian subgroup of the amphibole supergroup of the double chain inosilicate minerals with the ideal formula: Mg2(Mg3Al2)(Si6Al2)O22(OH)2
Gedrite is the magnesium (Mg) rich endmember of a solid solution series, with divalent magnesium cations readily replaced with ferrous iron (Fe), leading to the iron rich endmember 'ferrogedrite', with the formula: Fe2(Fe3Al2)(Si6Al2)O22(OH)2. However, pure endmembers are very rare, with often either one of the mentioned cations dominating the composition. Thus, the formula can be written in such a way to express common intermediary gerdite samples: (Mg,Fe)2(Mg,Fe)3Al2(Al2Si6O22)(OH)2.