Jahnsite-(MnMnFe)
Jahnsite-(MnMnFe) is an IMA-recognized mineral species in the phosphate class, with the chemical formula Mn²⁺Mn²⁺Fe²⁺₂Fe³⁺₂(PO₄)₄(OH)₂·8H₂O.
It crystallizes in the monoclinic crystal system (space group P2/a). It is a member of the Jahnsite structural group.
Key properties: Mohs hardness 4; specific gravity 2.654; Pale greenish brown streak; Vitreous luster; optically biaxial.
IMA symbol Jah-MnMnFe, IMA status: approved, named in 2018.
A low temperature, secondary mineral produced through alteration of primary phosphates in zoned granitic pegmatite.
It is found associated with Rockbridgeite, mitridatite.
Root name, Jahnsite, indicates a member of the group with M(3) = Fe3+; the suffix indicates sequentially the dominant atom in the X, M(1), and M(2) structural positions.