Barnesite Locality: Cactus Rat Mine, Cisco, Yellow Cat District (W. part of Thompsons District), Grand County, Utah, USA Original description: A 2.9 by 2.4 cms mass with reddish brown Barnessite. JSS specimen and photo. — Photo: John Sobolewski (JSS) · CC BY 3.0
Barnesite
Barnesite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula Na₂V⁵⁺₆O₁₆·3H₂O.
It crystallizes in the monoclinic crystal system (space group P2_1). It is a member of the Hewettite structural group.
Key properties: Mohs hardness 3; specific gravity 3.09–3.15; Adamantine, less brilliant after exposure luster; optically biaxial.
IMA symbol Bar, IMA status: approved, named in 1963.
Found in small cavities and fractures and as interstitial filling in sandstone in the oxidized zone of a vanadiferous uranium deposit, possibly formed as an oxidation product of hewettite (Cactus Rat mines, Utah, USA).
It is found associated with Metahewettite, thenardite (Cactus Rat mines, Utah, USA); bokite (The Fish, Nevada, USA); hewettite, metahewettite, jarosite, alunite, gypsum.
The mineral was named to honor Dr. William H. Barnes (1903–), National Research Council of Canada, Ottawa, Canada, authority on the crystallography of many vanadium minerals.