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Formula: (K)2(UO2)2(Si5O13).4H2O
Nesosilicate (insular SiO4 groups), uranyl mineral
Crystal System: Monoclinic
Specific gravity: 4.1 measured, 3.80 calculated
Hardness: 1 to 2
Streak: Yellow
Colour: Yellow
Common impurities: Al,Fe,Ca,Ba,Na,C
RADIOACTIVE
Environments
Igneous environments
Sedimentary environments
Weeksite occurs in opal veinlets in
rhyolite and
agglomerates,
as well as in sandstones and
limestones. Associated minerals include
opal, chalcedony,
calcite, gypsum,
fluorite, uraninite,
thorogummite, uranophane,
boltwoodite, carnotite and
margaritasite
(HOM, Dana).
Localities
At Chihuahua, Mexico, weeksite has been found associated with carnotite
on the dumps of an abandoned mercury mine, 4½ miles southwest of Lajitas,
Texas, USA
(AM 45.39-52).
At the Red Knob Mine, Muggins Mountains uranium prospects, Muggins Mining District, Muggins Mountains, Yuma county,
Arizona, USA, weeksite is associated with opal,
carnotite, vanadinite,
gypsum, calcite and
azurite
(AM 45.39-52).
Weeksite from the Red Knob Mine - Image
At an unnamed U occurrence at Inyo county, California, USA, weeksite has been found as a coating along fractures
in granite, associated with
uranophane
(AM 45.39-52).
At the Red Rock Mine, Plumas county, California, USA, weeksite is found in fractures in
rhyolite
(AM 45.39-52).
At the Jackpile Mine, Laguna subdistrict, Cibola County, New Mexico, USA, weeksite occurs in a
sandstone-type
deposit
(AM 45.39-52).
Weeksite from the Jackpile Mine - Image
At the Sherrer Quarry, C.K. Williams Quarry complex, Chestnut Hill, Easton, Northampton county, Pennsylvania, USA,
weeksite is found in fractures in limestone associated with
thorian uraninite, thorogummite,
uranophane, carnotite and
boltwoodite
(AM 45.39-52).
Weeksite from the Sherrer Quarry - Image
At the Mammoth Mine, Presidio county, Texas, USA, weeksite lines cavities in a welded
tuff
(AM 45.39-52).
The type locality is the Autunite No. 8 claim, Topaz Mountain, Thomas Range, Juab County, Utah, USA.
The oldest rock in the vicinity is a porphyritic
rhyolite containing numerous phenocrysts of
sanidine and quartz, some phenocrysts of
plagioclase and a few of biotite.
This rhyolite is overlain by a black glass welded
tuff consisting of pieces of pumice
and crystals of plagioclase and
biotite. This is overlain in turn by a white vitric
tuff containing volcanic rock fragments, mainly
pumice, and some tiny crystal fragments of
sanidine and quartz.
The weeksite occurs in numerous veinlets, up to 1/4 inch thick, which fill fractures in the
rhyolite. The veins consist chiefly of
opal, which fluoresces bright yellowish green. The only uranium mineral observed is
weeksite, which occurs in finely fibrous yellow rosettes, up to 1 mm across, both encrusted and intergrown with the
opal, and also on fracture surfaces free of opal.
Other vein minerals are calcite and
fluorite
(AM 45.39-52).
Weeksite from the Autunite No. 8 claim -
Image
At the Good Will property, Thomas Range, Juab Coounty, Utah, USA, uranium minerals are found in two types of occurrences:
disseminated in tuffaceous
sandstone and as replacement in
limestone cobbles in the
conglomerate which overlies the
sandstone. Uranophane-β, the
chief ore mineral, fills numerous pore spaces in the sandstone. The only
other uranium mineral noted in this rock was schröckingerite, which
occurredin a few veinlets in one pit.
Weeksite occurs in fine grains in the conglomerate, where it
replaces parts of limestone pebbles or cobbles. Weeksite occurs in
extremely fine grains and is the only mineral replacing the limestone
pebbles. No weeksite has been found in the uranium deposits in the underlying
tuffaceous sandstone,
and neither uranophane-β nor
schröckingerite has been found in the
conglomerate
(AM 45.39-52).
At the Silver Cliff Mine, Lusk, Niobrara county, Wyoming, USA, weeksite occurs in calcareous
sandstone with uranophane
(AM 45.39-52).
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