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Formula: NaCa3Mg2(As3+V4+2V5+10As5+6O51).45H2O
Polyoxometalate, arsenic- and
vanadium- bearing mineral
Crystal System: Triclinic
Specific gravity: 2.35 measured, 2.359 calculated
Hardness: 2
Streak: Green-blue
Colour: Dark green-blue
Environments
Sedimentary environments
Hydrothermal environments
Lumsdenite is a relatively new mineral, approved in 2018 and to date (May 2023) reported only from the type
locality
Localities
The type locality is the Packrat mine, Gateway, Mesa County, Colorado, USA. Lumsdenite is a polyoxometalate, which
is rare for a naturally occurring mineral, although they are important synthetic species. A polyoxometalate is a
compound that contains a cluster, or clusters, of three or more transition-metal-centered polyhedra that link by sharing
oxygen atoms between and among the polyhedra. The Colorado Plateau is host to many such minerals.
Lumsdenite contains a [As3+V4+,5+12As5+6O51]
heteropolyanion that also occurs in the structures of vanarsite,
packratite, gatewayite and
morrisonite; together, these minerals constitute the
vanarsite mineral family. They are found in the same unusual post-mining
secondary assemblage rich in
vanadium and arsenic as is found on
the main tunnel level of the Packrat mine. Lumsdenite forms from the oxidation of
montroseite-corvusite assemblages
in a moist environment. 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 (quite acid). Lumsdenite is very rare; it has so far been found on only one specimen. It occurs
on bitumen associated with montroseite- and
corvusite-bearing sandstone.
Other secondary minerals found in close association with
lumsdenite are gypsum,
huemulite, rosslerite, and at
least two other potentially new minerals
(CM 58.1.137–151).
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