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Formula: Cu(UO2)2(PO4)2.12H2O
Hydrated phosphate, autunite group,
uranyl mineral
Crystal System: Tetragonal
Specific gravity: 3.22 measured
Hardness: 2 to 2½
Streak: Green
Colour: Emerald green
Solubility: Moderately soluble in hydrochloric, sulphuric and nitric acid
Common impurities: Ca,Ba,Mg
RADIOACTIVE
Environments:
Pegmatites
Hydrothermal environments
Uranium is a highly soluble, radioactive, heavy metal. It can be dissolved
easily and transported by ground waters.
Also, it does not usually form very insoluble mineral species, which is a further factor in the wide variety of
environments and localities in which uranium minerals accumulate.
Within magmas uranium is an incompatible element (ie its size and charge do
not allow it to combine easily with other components of the melt), and so the last part of
granite melts to crystallise tends to become highly enriched in
uranium, thorium and potassium and their compounds.
Uraninite is the most important ore of
uranium, and torbernite and
autunite are less important.
(Wiki)
Torbernite is a
secondary mineral found in the oxidation zones of some
uranium-rich copper deposits, and
as a coating of fissures in
granite. It forms as an alteration product of
uraninite or other
uranium-bearing
minerals, and it is associated with uraninite,
autunite, carnotite
and other phosphate minerals.
The copper Cu in the structure can be replaced by calcium Ca, forming
autunite.
Above 60oC torbernite dehydrates to metatorbernite.
Localities
At the Block 14 Open Cut, Broken Hill, New South Wales, Australia, a few small crystals of torbernite have been
found on
pyromorphite crusts.
(AJM 3.1.53)
Torbernite from Block 14 open cut - Image
At the South Alligator Valley Uranium Field, Northern Territories, Australia, the rare mineral
threadgoldite is found coating or
intergrown with torbernite/metatorbernite.
(AJM 11.1.9)
At the Mount Isa Block, Queensland, Australia, just one small crystal of torbernite has been reported, associated with
malachite.
(AJM 17.2.86)
At the Mount Painter uranium deposit, Flinders Ranges, South Australia, torbernite of
supergene origin occurs
associated with ironstone (iron-rich sedimentary rock) and sometimes minor
fluorite, baryte and
quartz.
(https://d28rz98at9flks.cloudfront.net/9761/Rec1945_067.pdf)
Torbernite from Mount Painter - Image
At the Hagendorf pegmatite, Bavaria, Germany, the dissolution of
rockbridgeite
releases (PO4)2- which leads to the precipitation of
bassetite and then torbernite. In the presence of minor
manganese,
lehnerite may form, and in
the presence of calcium, autunite may form.
( MM 71.4.371-387)
metatorbernite occur in about equal proportions. Epitactic
overgrowths of autunite on
torbernite/metatorbernite have been found, and rare
microcrystalline
drusy crusts of jarosite. Baryte also occurs
rarely in association with autunite and torbernite.
(R&M 87.3.270-276)
Torbernite from the Apex mine - Image
At the Keyes Mica Quarries, Orange, Grafton County, New Hampshire, USA, the
pegmatites are beryl-type
rare-element (RE) pegmatites.
The Number 1 mine exposed a pegmatite that shows the most
complex zonation and diverse mineralogy of any of the Keyes
pegmatites. Six zones are distinguished, as follows, proceeding
inward from the margins of the pegmatite:
(1) quartz-muscovite-plagioclase
border zone, 2.5 to 30.5 cm thick
(2) plagioclase-quartz-muscovite
wall zone, 0.3 to 2.4 metres thick
(3) plagioclase-quartz-perthite-biotite
outer intermediate zone, 0.3 to 5.2 metres thick, with lesser muscovite
(4) quartz-plagioclase-muscovite
middle intermediate zone, 15.2 to 61.0 cm thick
(5) perthite-quartz inner intermediate zone, 0.9 to 4.6 meters thick
(6) quartz core, 1.5 to 3.0 metres across
The inner and outer intermediate zones contained perthite crystals up to
1.2 meters in size that were altered to vuggy
albite-muscovite with
fluorapatite crystals. This unit presumably was the source of the
albite, muscovite,
fluorapatite, quartz and other
crystallised minerals found in pieces of vuggy albite
rock on the dumps next to the mine.
The middle intermediate zone produced sheet mica with accessory minerals including
tourmaline, graftonite,
triphylite, vivianite,
pyrite, pyrrhotite, and
beryl crystals to 30.5 cm long and 12.7 cm across.
A specimen of microsized green torbernite crystals has been collected at one of the Keyes mines.
Muscovite and pale blue
fluorapatite crystals in the matrix indicate that this specimen probably
came from the No. 1 mine
(R&M 97.4.325-326).
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