Ferristrunzite Locality: B224 Road cut, Aprath castle, Wuppertal, North Rhine-Westphalia, Germany Collected in 1989. Field of view 4 mm. Specimen and photo Leon Hupperichs. — Photo: Leon Hupperichs · CC BY-SA 3.0
Ferristrunzite
Ferristrunzite is an IMA-recognized mineral species in the phosphate class, with the chemical formula Fe³⁺Fe³⁺₂(PO₄)₂(OH)₃·5H₂O.
It crystallizes in the triclinic crystal system. It is a member of the Strunzite structural group.
Key properties: specific gravity 2.38–2.5; Very pale yellow streak; optically biaxial.
IMA symbol Fstz, IMA status: approved, named in 1986.
Found as a rare secondary mineral in argillaceous and clastic sediments, probably as an oxidation product of strunzite (Blaton, Belgium).
It is found associated with Beraunite, crandallite, diadochite, allophane–evansite, strengite, phosphosiderite, cacoxenite (Blaton, Belgium).
The name refers to ferric iron in the composition and its relation to strunzite.