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Formula: CeBSiO5
Nesosilicate (insular SiO4 groups), borosilicate,
cerium-bearing mineral
Crystal System: Trigonal
Specific gravity: 4.57 to 4.60 measured, 4.67 calculated
Hardness: 6½
Streak: White
Colour: Pale violet-grey, light pink, brownish yellow, orange
Solubility: No reaction in acids
Common impurities: Th,Ca,Al
Weakly RADIOACTIVE
Environments
Volcanic igneous environments
Pegmatites
Metamorphic environments
Hydrothermal environments
Stillwellite-(Ce) occurs in
garnet-diopside
skarn formed between
granodiorite and
granulite, also in magnetite
ore, in pegmatites and hydrothermal veins associated with
alkalic rocks and in volcanic ejecta
(Dana).
Localities
At the type locality, the Mary Kathleen Mine, Mary Kathleen district, Rosebud Station, Cloncurry Shire, Queensland,
Australia, stillwellite-(Ce) occurs in quantity in crystals up to 5 mm in diameter as a major constituent of
radioactive ore. It is associated with much allanite and with
garnet as a metasomatic replacement of metamorphosed calcareous sediments.
Uraninite is dispersed in allanite
and stillwellite-(Ce)
(AM 41.370-371).
At the Desmont Mine, Monmouth Township, Haliburton County, Ontario, Canada, stillwellite-(Ce) is associated
with calcite, monazite-(Ce),
bastnäsite, thorite,
uranothorite and thorianite
(HOM).
At the Dara-i-Pioz Glacier, Districts of Republican Subordination, Tajikistan, stillwellite-(Ce) occurs in
alkalic pegmatites in
syenite in an alkalic massif. Associated minerals include
pyrochlore, tienshanite,
sogdianite, thorite,
kupletskite-(Cs),
reedmergnerite, steacyite,
pectolite and quartz
(HOM).
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