Greifensteinite (Picture size: 3 mm) Locality: Greifensteine, Ehrenfriedersdorf, Ore mountains, Saxony, Deutschland — Photo: Leon Hupperichs · CC BY-SA 3.0
Greifensteinite
The ferrous-iron member of the roscherite group — a beryllium phosphate forming dark olive-green monoclinic prisms.
Intro adapted from Wikipedia (CC BY-SA).
Greifensteinite is an IMA-recognized mineral species in the phosphate class, with the chemical formula Ca₂Be₄Fe²⁺₅(PO₄)₆(OH)₄·6H₂O.
It crystallizes in the monoclinic crystal system (space group C2/c). It is a member of the Roscherite structural group.
Key properties: Mohs hardness 4.5; specific gravity 2.93; White streak; Vitreous luster; refractive index 1.632; optically biaxial.
IMA symbol Gfs, IMA status: approved, named in 2001.
Found in miarolitic cavities in Li-rich granite pegmatite.
It is found associated with Albite, K-feldspar, roscherite, viitaniemiite, childrenite, quartz, an apatite-group mineral, herderite, elbaite, montmorillonite.
The name is derived from the locality in Germany that provided the first specimens.