Chamosite
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Chamosite is the Fe²⁺end member of the chlorite group. A hydrous aluminium silicate of iron, which is produced in an environment of low to moderate grade of metamorphosed iron deposits, as gray or black crystals in oolitic iron ore. Wikipedia
Crystal class: Prismatic (2/m); (same H-M symbol)
Crystal system: Monoclinic
Formula (repeating unit): (Fe2+,Mg)5Al(AlSi3O10)(OH)8
Mohs scale hardness: 3
Space group: C2/m