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Formula: Ca6(As3+V4+3V5+9As5+6O51).31H2O
Polyoxometalate mineral, 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: 2.34 measured, 2.337 calculated
Hardness: 2
Streak: Greyish blue
Colour: Very dark greenish blue
Luminescence: Nonfluorescent under UV
Solubility: Insoluble in water at room temperature, easily soluble in dilute hydrochloric acid at room temperature
Environments
Sedimentary environments
Hydrothermal environments
Gatewayite is a new mineral, approved in 2015 and to date (November 2022) 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.
Gatewayite 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+.
Gatewayite blades are up to 0.5 mm long and form divergent intergrowths; the mineral also occurs as crude
prisms, up to 1 mm long, with rounded faces, and as composite crystals consisting of subparallel intergrowths of
narrow prisms up to 2 mm long
(CM 54.1.145-162).
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