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Formula: LaAl3(PO4)2(OH)6
Anhydrous phosphate, plumbogummite group,
alunite supergroup,
lanthanum-bearing mineral
Crystal System: Trigonal
Specific gravity: 3.52 measured, 3.71 calculated
Hardness: 5 to 6
Colour: Colourless to pale yellow, white in aggregates
Weakly RADIOACTIVE
Environments
Localities
At the type locality, the Shituru Mine, Likasi, Haut-Katanga, DR Congo, florencite-(La) occurs as euhedral,
colourless to pale yellow crystals normally not exceeding 30 µm across in
siltstones belonging to an intertidal facies and overlain by
lagoonal dolostone. Associated minerals include
apatite, clay minerals,
dolomite, hematite,
quartz, rutile and
zircon
(Mindat).
At Bangombé, Léboumbi-Leyou Department, Haut-Ogooué Province, Gabon, spontaneous fission reactions occurred in
uranium deposits approximately 2 billion years ago and lasted 105 to 106 years, producing a
substantial amount of fission products. The Bangombe fission reactor, discovered in 1985, is in
sandstone at a depth of 12 m and consists of a 5 cm thick body of
a massive uranium ore (the reactor's "core"), which is overlain by a 30 cm
thick clay mantle.
Florencite-(La) and florencite-(Ce) have been identified in
illite from the clay mantle and
in sandstone beneath the reactor zone, respectively.
Florencite-(Ce) is apparently unrelated to nuclear processes and
occurs with monazite-(Ce),
apatite, Ti02 (probably
anatase),
zircon and illite. Grains of
florencite-(Ce) contain inclusions of
thorite, chalcopyrite, and
galena.
Florencite-(La) was found 5 cm from the "core" of the
reactor and contains inclusions of galena and
uranium-titanium -bearing phases.
Secondary uraninite
and coffinite have precipitated on some of the florencite grains.
Grains of florencite contain numerous inclusions of thorite,
chalcopyrite and galena.
Though monazite grains are heavily corroded and altered, they are not
replaced by florencite. In areas where monazite and
florencite are in physical contact, the latter is an overgrowth on
monazite. Apatite grains are
corroded; they have not been seen in physical contact with florencite.
The florencite-(La)-bearing sample from the reactor zone consists of
illite with veinlets and aggregates of authigenic (formed in place)
ferromagnesian chlorite. One of the numerous fractures divides this
sample into two portions: one contains florencite, galena, nodules
of solid bitumens associated with
titanium-, zirconium- and
vanadium- rich phases, and
uranium minerals coffinite and
uraninite. The other portion contains abundant
pyrite and detrital zircon dispersed
within illite. Florencite is embedded in the brownish
illite and occurs as a train of elongated overgrowths of colourless to
yellowish rhombohedral crystals up to 110 microns long and 50 microns wide. Some florencite grains contain
inclusions of galena and vanadium-
and titanium-bearing phases.
Uraninite and coffinite
precipitated on florencite and replaced it along fractures. Precipitation of
uraninite on florencite and adjacent
illite a few centimetres outside the reactor core suggests that this is a
secondary uraninite
(AM 81.1263-1269).
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