Formula: NaCa3Mg2(As3+V4+2V5+10As5+6O51).45H2O
Specific gravity: 2.35 measured, 2.359 calculated
Hardness: 2
Streak: Green-blue
Colour: Dark green-blue

Sedimentary environments
Hydrothermal environments

Lumsdenite is a relatively new mineral, approved in 2018 and to date (April 2022) reported only from the type locality


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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