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Formula: Ca11(As3+V5+10V4+2As5+6O51)2 .83H2O
Polyoxometalate mineral, arsenic- and
vanadium- bearing
A polyoxometalate is a polyatomic ion, usually an anion, that consists of three or more transition metal oxyanions
linked together by shared oxygen atoms to form closed 3-dimensional frameworks (Wiki).
Crystal System: Triclinic
Specific gravity: 2.36 measured, 2.351 calculated
Hardness: 2
Streak: Greyish blue
Colour: Very dark greenish blue
Luminescence: Nonfluorescent under UV
Solubility: At room temperature, insoluble in water and easily soluble in dilute hydrochloric acid
Environments
Sedimentary environments
Hydrothermal environments
Packratite was approved in 2014 but to date (February 2023) it has been reported only from the type locality.
Localities
At the type locality, the Packrat Mine, Gateway, Mesa County, Colorado, USA,
vanarsite, packratite,
morrisonite and gatewayite
were found in the main tunnel level.
The Packrat mine is in the Uravan Mineral Belt, in which uranium and vanadium
minerals occur together on montroseite- and
corvusite-bearing sandstone.
They are also closely associated with pharmacolite and a potentially new
vanadate mineral. Other
secondary minerals found in the mine include
andersonite, ansermetite,
calcite, dickthomssenite,
gypsum, hewettite,
hummerite, lasalite,
magnesiopascoite, martyite,
munirite, navajoite,
pascoite, picropharmacolite,
postite, rossite, native
selenium, sherwoodite and
uranopilite.
Packratite forms from the oxidation of
montroseite-corvusite
assemblages in a moist environment. Mining operations have exposed unoxidised and oxidised phases. Under ambient
temperatures and generally oxidising near-surface conditions, water reacts with
pyrite and an unknown arsenic-bearing
phase (perhaps arsenopyrite) to form aqueous solutions with relatively
low pH (acid). The various secondary
vanadate phases that form depend upon prevailing conditions and the presence
of other cations such as Na+, Ca2+ and Mg2+.
Packratite occurs as blades up to about 1 mm long, striated lengthwise, and grown in sub-parallel and
divergent intergrowths, also occurs as pearly green, botryoidal aggregates
(CM 54.1.145-162).
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