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Formula: Ca11(As3+V4+2V5+10As5+6O51)2.78H2O
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: Monoclinic
Specific gravity: 2.29 measured, 2.221 calculated
Hardness: 2½
Streak: Greyish blue
Colour: Very dark blue
Environments
Sedimentary environments
Hydrothermal environments
Morrisonite was approved in 2014 but to date (June 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.
Morrisonite 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+.
Morrisonite occurs as blades up to about 1 mm long, striated lengthwise, and grown in sub-parallel and
divergent intergrowths
(CM 54.1.145-162).
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