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Formula: NaCa12(As3+V5+8.5V4+3.5As5+6O51)2.78H2O
Polyoxometalate, arsenic and
vanadium bearing mineral.
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: Monoclinic
Specific gravity: 2.48 measured, 2.460 calculated
Hardness: 2
Streak: Greyish blue
Colour: Very dark blue
Luminescence: No fluorescence under UV
Solubility: Insoluble in water at room-temperature, easily soluble in dilute hydrochloric acid at
room-temperature
Environments
Vanarsite is a relatively new mineral, approved in 2014 and to date (December 2023) reported only from
the type locality
Localities
At the type locality, the Packrat Mine, Beaver Mesa, Gateway Mining District, Mesa County, Colorado, USA,
vanarsite, packratite,
morrisonite and gatewayite
were newly reported in 2016. Crystals of all four minerals are very dark blue to greenish blue blades. They are
found together on montroseite-and
corvusite- bearing
sandstone in association with
pharmacolite. Vanarsite is monoclinic,
packratite is triclinic,
morrisonite is monoclinic, and
gatewayite is also monoclinic. The structures of all four new minerals
contain the novel polyoxometalate-like heteropolyanion,
[As3+As5+6V4+2+xV5+10–xO51](11+x)–
(x = 0 to 1.5)
which is new to science.
At the Packrat mine uranium and
vanadium minerals occur together in deposits in
sandstone. The mine site is currently inactive. The samples of the
new minerals were collected in 2011 and 2013. 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.
The new minerals form 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)
to form various secondary
vanadate phases
(CM 54.1.145-162)
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