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Formula: Na2V5+6O16.3H2 O
Hydrated vanadate,
hewettite group
Crystal System: Monoclinic
Specific gravity: 3.09 to 3.15 measured, 3.23 calculated
Hardness: 3
Streak: Brownish red
Colour: Brilliant dark red; brownish red on exposure
Solubility: Slowly soluble in dilute hydrochloric acid
Common impurities: Ca
Environments
Sedimentary environments
Hydrothermal environments
Localities
Barnesite occurs in several mines of the Kurumsak and Balasauskandyk districts, northwestern Kara-Tau Mountains,
Kazakhstan, in weathered black schist. Associated minerals include
hewettite, metahewettite,
jarosite, alunite,
gypsum and baryte
(HOM ).
At The Fish, Gibellini Mining District, Eureka County, Nevada, USA, barnesite is associated with
bokite
(HOM ).
At the type locality, the Cactus Rat mine, The Poison Strip, Thompsons Mining District, Grand County, Utah, USA, the
deposit occurs in sandstone. Barnesite is brilliant, dark red
with an adamantine lustre when it is fresh, and it forms microscopic bladed to fibrous crystals. On exposure, the
colour becomes slightly brownish red, and the lustre decreases somewhat. It forms small clusters of subparallel to
radiating fibres as well as continuous coatings of
bedding plane fractures or small cavities where fragments of wood have weathered out
(AM 48.1187-1195).
The barnesite occurs in the oxidised zone of the vanadiferous
uranium
deposit, possibly formed as an oxidation product of hewettite; other
associates include metahewettite and
thénardite
(HOM).
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