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Formula: CaV5+6O16.9H2O
Vanadate, hewettite group
Crystal System: Monoclinic
Specific gravity: 2.51 to 2.61 measured, 2.67 calculated
Hardness: Extremely soft
Streak: Brownish red
Colour: Deep red; chocolate brown (upon exposure); red to orange in transmitted light
Solubility: Slightly soluble in water
Environments
Hewettite is a secondary mineral resulting from the alteration of
patronite, or from the alteration of less-oxidised vanadium
minerals in Colorado Plateau-type uranium-vanadium deposits, where it is associated with
carnotite, corvusite,
fervanite, metahewettite,
montroseite, navajoite,
rauvite, steigerite and
tyuyamunite. It may reversibly dehydrate to
metahewettite.
(Mindat, HOM).
Localities
The type locality, the Ragra Mine, Huayllay District, Pasco Province, Pasco, is a very rich vanadium
deposit in sedimentary rocks.
Here hewettite is an alteration product of patronite and occurs associated with it
(Mindat, HOM).
At the Gallagher Vanadium Property, Cochise County, Arizona, USA, hewettite has been seen on the dump as individual
1–2-mm crystals and as fibrous mats associated with weathered vanadinite and
calcite
(R&M 90-4.343).
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