Packratite

packratite

vanarsite

morrisonite

gatewayite

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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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