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Formula: (UO2)6(SO4)O2(OH)6.14H2O
Hydrated sulphate, uranyl mineral
Crystal System: Triclinic
Specific gravity: 3.7 to 4.0 measured, 3.74 calculated
Colour: Bright yellow, straw-yellow, colourless to light yellow in transmitted light
Solubility: Insoluble in water, soluble in dilute acids
Luminescence: Uranopilite fluoresces bright greenish yellow, in both long and short wave UV
RADIOACTIVE
Environments
Sedimentary environments
Hydrothermal environments
Uranopilite is a secondary mineral and in part at least
is of recent formation as an efflorescence on the walls of mine workings. It commonly occurs as a coating on oxidised
vein material in which uraninite and sulphides were
primary constituents.
Gypsum and zippeite are common
associates, and other associates include uraninite,
johannite, uranophane,
soddyite and fourmarierite.
The uranopilite forms fragile, small-botryoidal crusts or isolated, globular to reniform incrusting masses of
small size. These are composed of tiny lathlike or needlelike crystals that form felted aggregates. It may dehydrate
to metauranopilite
(AM 37.950-959, HOM).
Localities
At Hottah Lake, Northwest Territories, Canada, uranopilite has been identified as thin coatings on altered
pitchblende. This material is relatively fine-grained with a pale yellow
colour and a feltlike structure
(AM 37.950-959).
At Great Bear Lake, North Slave Region, Northwest Territories, Canada, uranopilite occurs very sparsely as
thin, feltlike crusts and films on massive pitchblende. The
uranopilite is relatively dense and fine-grained,
with a straw-yellow to pale yellow colour and a dull-silky lustre. It is associated with minor amounts of
zippeite as golden-yellow crusts, and with tiny radial-fibrous globules of
johannite, fourmarierite
and erythrite
(AM 37.950-959).
At the Jánská vein, Březové Hory deposit, Březové Hory, Příbram, Příbram District, Central Bohemian Region, Czech
Republic, phosphate-rich metalodèvite has been found. The vein has
been intensively exploited for silver and is noted for its
uranium mineralisation. Specimens of massive
uraninite and gummite have been
found in this vein, along with cuprosklodowskite,
metatorbernite, masuyite,
wölsendorfite, anglesite,
kasolite, zinczippeite and
other minerals of the zippeite group,
compreignacite, uranopilite,
uranophane and widenmannite
(CM 48.113-122).
There are two co-type localities, Jáchymov, Karlovy Vary District, Karlovy Vary Region, Czech Republic and
Johanngeorgenstadt, Erzgebirgskreis, Saxony, Germany.
Jáchymov, Karlovy Vary District, Karlovy Vary Region, Czech Republic, is a co-type locality.
Uranopilite from Jáchymov - Image
At the co-type locality Johanngeorgenstadt, Erzgebirgskreis, Saxony, Germany, uranopilite is a product of the decomposition of
pitchblende that was found in the oxidation zones of
uranium-bearing veins. Massive specimens sometimes retain unaltered
pitchblende cores. Uranopilite also occurs as pale yellow to
yellow velvety crusts and as reniform to fibrous aggregates. Attractive specimens were found particularly in the
Gottes Segen pit, the Silberhoffnungs bed and the Jonas bed. Sometime around 1859, magnificent specimens of botryoidal
uranopilite were recovered, with individual botryoids up to 1 cm across
(Minrec 55.5.624).
At the Apex Mine, Reese River Mining District, Lander County, Nevada, USA, the No. 1 and No. 2 adits formerly provided
rather spectacular specimens of uranopilite associated with zippeite
and rutherfordine. Here, uranopilite is present as bright
lemon-yellow, flatlying, radiating crystals to 1 mm. The species may occur either directly upon matrix or as a
common overgrowth upon earlier-formed rutherfordine
(R&M 87.3.276).
Uranopilite from the Apex mine - Image
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