Argandite
Argandite is an IMA-recognized mineral species in the vanadate class, with the chemical formula Mn₇(VO₄)₂(OH)₈.
It crystallizes in the monoclinic crystal system (space group P2_1/n). It is a member of the Allactite structural group.
Key properties: Mohs hardness 3.5–4; specific gravity 3.71; Pale orange streak; Vitreous luster; optically biaxial.
IMA symbol Agd, IMA status: approved, named in 2010.
Found in a metamorphosed (upper greenschist facies) lens of synsedimentary exhalative Mn-Fe ore enriched in V relative to As in dolomitic marble.
It is found associated with Pyrobelonite, reppiaite.
The mineral was named to honor Swiss geologist Émile Argand (1879-1940) for his contribution to understanding Alpine geology in general and the geology of Turmanntal in particular.