Jahnsite-(NaMnMg)
Jahnsite-(NaMnMg) is an IMA-recognized mineral species in the phosphate class, with the chemical formula (Na,Ca)(Mn²⁺,Fe³⁺)(Mg,Fe³⁺)₂Fe³⁺₂(PO₄)₄(OH)₂(H₂O)₈.
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 2.68–2.69; Very pale yellow streak; Vitreous luster; optically biaxial.
IMA symbol Jah-NaMnMg, 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 Frondelite, albite, meurigite-K, phosphosiderite, strengite (Sapucaia); phosphosiderite, ushkovite, strunzite, bermanite (White Rock).
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.