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Formula: [(UO2)(SO4)(H2O)2]2.H2O
Hydrated uranyl sulphate
Crystal system: Monoclinic
Specific gravity: 3.844 calculated for the empirical formula
Hardness: 2
Streak: White
Colour: Pale greenish yellow
Luminescence: Bright greenish white fluorescence under long wave and short wave UV - Only Utah specimens
Solubility: slightly deliquescent; easily soluble in water at room temperature
Environments
Shumwayite is a relatively new mineral, approved in 2015. It occurs in efflorescent crusts formed by
hydration-oxidation weathering of primary
uranium minerals, especially
uraninite, by acidic solutions derived from the decomposition of
associated sulphides
(HOM).
Localities
There are two co-type localities, the Giveway-Simplot Mine and the Green Lizard Mine, both in the Red Canyon Mining
District, San Juan County, Utah, USA.
At the Red Canyon Mining District, shumwayite was first discovered on specimens collected underground in the
Green Lizard mine; later it was identified on specimens collected underground in the Giveaway-Simplot mine.
Mineralised channels are in the Shinarump member of the Chinle Formation. The Shinarump member consists of medium-
to coarse- grained sandstone,
conglomeratic
sandstone beds and thick
siltstone lenses. Ore minerals were deposited as replacements of
wood and other organic material, and as disseminations in the enclosing
sandstone. Since the mine closed, oxidation of
primary ores in the humid underground environment has
produced a variety of secondary minerals, mainly
sulphates, as efflorescent crusts on the surfaces of mine walls. Shumwayite is a relatively rare mineral in
the secondary uranyl
sulphate mineral assemblages.
At the Green Lizard mine, shumwayite is usually found on
sandstone and is associated with
calcite, gypsum,
plášilite, pyrite,
rozenite and sulphur. Other
secondary minerals thus far found in the Green Lizard mine
assemblage include beshtauite,
boussingaultite, fermiite,
johannite, natrozippeite,
oppenheimerite,
wetherillite and several other potentially new
uranyl sulphate minerals.
At the Giveaway-Simplot mine, shumwayite is usually found on asphaltum (bitumen) and is associated with
rietveldite, rhomboclase
and römerite.
Uranyl sulfate minerals typically form by hydration–oxidation weathering of
primary uranium
minerals, mainly uraninite, by acidic solutions derived from the
decomposition of associated sulphides. Shumwayite and other
secondary minerals occurring in the efflorescent crusts of
the Green Lizard and Giveaway-Simplot mines have formed by such a process.
Shumwayite forms pale greenish-yellow monoclinic prisms, often irregular and more or less rounded, up to
∼0.3 mm long. Crystals commonly occur in subparallel to random intergrowths
(MM 81.2.273-285).
Shumwayite from the Giveaway-Simplot Mine -
Image
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