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Formula: U4+O2
Simple oxide of uranium,
uraninite group, forms a series with
thorianite
Pitchblende is a massive, often globular, possibly impure, variety of uraninite.
Crystal System: Isometric
Specific gravity: 10.63 to 10.95 measured, 10.88 calculated
Hardness: 6
Streak: Black
Colour: Black, grey, brownish
Solubility: Slightly soluble in hydrochloric acid; moderately soluble in sulphuric and nitric acid
Common impurities: Th,Zr,Pb,Ra,Ac,Po,Ce,Y,Er,La
RADIOACTIVE
Environments:
Emmons pegmatitePegmatites
Sedimentary environments
Hydrothermal environments
Uraninite occurs as a primary mineral in several
distinct geological settings:
1. In pegmatites, typically as well-formed crystals or
dendritic growths associated with monazite,
columbite-tantalite
and zircon.
2. In high temperature hydrothermal veins, typically as massive pitchblende associated with
cassiterite, arsenopyrite
and cobalt - nickel -
bismuth - arsenic minerals.
3. In moderate temperarure hydrothermal veins with galena and other sulphides.
4. In sandstone deposits with
vanadium, copper and other metal
ores.
In pegmatites uraninite crystals contain up to ~10%
thorium and ~15%
rare earth elements. This is because the size and valence of
these ions prevent their inclusion in the main rock-forming silicates as they crystallise. Pitchblende, on
the other hand, is usually fairly pure because it has crystallised from a hydrothermal fluid that does not contain
these elements. Both varieties of uraninite contain up to ~20% of radiogenic
lead, depending on the age of the deposit
(Lauf2).
Localities
At the Eldorado mine, Great Bear Lake, Northwest Territories, Canada, uraninite occurs in veins with native
silver
(Dana).
Uraninite from the Eldorado Mine -
Image
At the Shinkolobwe Mine, Shinkolobwe, Kambove District, Haut-Katanga, DR Congo, good specimens of sheet and wire
gold associated with uraninite have been
(R&M 96.3.220).
Uraninite from Shinkolobwe - Image
The type locality is Jáchymov, Karlovy Vary District, Karlovy Vary Region, Czech Republic.
Uraninite from Jáchymov - Image
At Johanngeorgenstadt, Erzgebirgskreis, Saxony, Germany, uraninite was found as the amorphous variety
pitchblende, in black, pitchy, collomorphic masses with reniform (kidney-shaped) surfaces. It often shows a
characteristic radial structure and concentric shrinkage cracks filled with
pyrite, chalcopyrite,
galena, skutterudite,
quartz, calcite,
hematite or chlorite. Associated
minerals include cobalt-nickel
arsenides, löllingite,
native bismuth, galena,
chalcopyrite, pyrite,
hematite, fluorite,
quartz, chert,
dolomite, ankerite and
calcite, more rarely silver minerals
and native arsenic
(Minrec 55.5.623).
At Placeres de Guadalupe, Chihuahua, Mexico, uraninite occurs with gold
(Dana).
At the Longs Peak - St Vrain batholith near Jamestown, Jamestown District, Boulder county,
Colorado, USA, centimetre to decimetre sized mineralised pods and veins consist of zoned
mineral assemblages dominated by fluorbritholite-(Ce)
in a core 10 cm thick, with monazite-(Ce),
fluorite and minor quartz,
uraninite and sulphides. The core is surrounded by a
typically millimetre thick rim of allanite-(Ce), with
minor monazite-(Ce) in the inner part of the rim.
Bastnäsite-(Ce),
törnebohmite-(Ce) and
cerite-(Ce) appear in an intermediate zone between core and
rim, often just a few hundreds of microns wide
(R&M 96.3.252-253).
At the Emmons pegmatite, Greenwood, Oxford county, Maine, USA, uraninite has been found rarely in massive
microcline, commonly replaced by
schoepite-group minerals and other secondary uranium minerals. In the proximity of
uraninite, autunite and meta-autunite
are seen. The Emmons pegmatite is situated in a belt of metasedimentary rocks which originated as marine sediments which were
subsequently deformed and metamorphosed. The Emmons pegmatite is a highly evolved
boron-lithium-cesium-tantalum
enriched pegmatite
(R&M 94.6.516).
At the pegmatites on Noyes Mountain, Greenwood, Oxford county,
Maine, USA, uraninite is found
in a garnet layer in masses to 1.5 cm, associated with
coffinite and less commonly with
autinite and
meta-autinite. Accessory zircon,
monazite and xenotime group species are intimately
associated with the uranium assemblage
(R&M 95.3.271).
At the the Chickering Mine, Walpole, Cheshire County, New Hampshire, USA, a single sample of uraninite has been found with
zircon in a pegmatite
(R&M 90.5.421).
At the Ruggles pegmatite, Grafton county, New Hampshire, USA, uraninite occurs intergrown with
albite-rich feldspar or with
muscovite, and associated
with smoky quartz, curite and
uranophane
(Dana, AM 23.334-341).
Uraninite from the Ruggles Mine - Image
At Baringer hill, Llano county, Texas, USA, uraninite occurs in a pegmatite with gadolinite
(Dana).
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