White fibrous spheres of nordgauite and yellow crystals of rittmannite. Ex Jürgen Kastning collection. From: Silbergrube, Waidhaus, Neustadt an der Waldnaab, Upper Palatinate, Bavaria, Germany. — Photo: Leon Hupperichs · CC BY-SA 3.0
Rittmannite
Rittmannite is an IMA-recognized mineral species in the phosphate class, with the chemical formula (Mn²⁺,Ca)Mn²⁺(Fe²⁺,Mn²⁺,Mg)₂(Al,Fe³⁺)₂(PO₄)₄(OH)₂·8H₂O.
It crystallizes in the monoclinic crystal system (space group P2/a). It is a member of the Jahnsite structural group.
Key properties: Mohs hardness 3.5; specific gravity 2.81; White streak; Vitreous luster; optically biaxial.
IMA symbol Rit, IMA status: approved, named in 1987.
Found as a very rare mineral in phosphatic nodules in zoned granite pegmatite veins (Mangualde pegmatite, Portugal).
It is found associated with Kryzhanovskite, frondelite, huréaulite, orthoclase (Mangualde pegmatite, Portugal).
The mineral was named to honor Professor Alfred Rittmann (1893–1980), German petrologist and volcanologist, University of Catania, Catania, Italy.