Zwieselite , Quartz Dimensions: 61 mm × 58 mm × 38 mm Locality: Hagendorf South Pegmatite, Hagendorf, Waidhaus, Neustadt an der Waldnaab District, Upper Palatinate, Bavaria, Germany Description: Brown zwieselite and white quartz. — Photo: Pascal Ollic · Public domain
Zwieselite
Zwieselite is an IMA-recognized mineral species in the phosphate class, with the chemical formula Fe²⁺₂(PO₄)F.
It crystallizes in the monoclinic crystal system (space group I2/a). It is a member of the Triplite structural group.
Key properties: Mohs hardness 5–5.5; specific gravity 3.89–3.97; Vitreous to resinous luster; optically biaxial.
IMA symbol Zwi, IMA status: approved, named in 1841.
A primary phosphate in complex zoned granite pegmatites.
It is found associated with Triphylite, huréaulite, rockbridgeite.
The name refers to its first-noted occurrence at Hühnerkobel, nearby Zwiesel and Rabenstein, Germany.