Stewartite Locality: Hagendorf South Pegmatite (Cornelia Mine; Hagendorf South Open Cut), Hagendorf , Waidhaus , Vohenstrauß , Oberpfälzer Wald , Upper Palatinate , Bavaria , Germany ( Locality at mindat.org ) Picture width 1,5 mm. Collection and photograph Christian Rewitzer — Photo: Christian Rewitzer · CC BY-SA 3.0
Stewartite
Stewartite is an IMA-recognized mineral species in the phosphate class, with the chemical formula Mn²⁺Fe³⁺₂(PO₄)₂(OH)₂·8H₂O.
It crystallizes in the triclinic crystal system (space group P-1). It is a member of the Stewartite structural group.
Key properties: specific gravity 2.94; optically biaxial.
IMA symbol Stw, grandfathered status — known before the IMA’s founding, named in 1912.
A rare oxidation product formed by the leaching of primary phosphates in complex zoned granite pegmatites.
It is found associated with Lithiophilite, triphylite, huréaulite, strunzite, laueite, pseudolaueite, eosphorite, rockbridgeite, strengite, diadochite, phosphosiderite, Fe–Mn oxides.
The name refers to its originally noted occurrence at the Stewart mine, Pala, California, USA.