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Formula: Y3Si3O10F
Sorosilicate (Si2O7 groups), yttrium-bearing mineral
Crystal System: Monoclinic
Specific gravity: 4.2
Hardness: 6
Streak: White
Colour: Flesh-pink, brown or greenish
Solubility: Soluble in hydrochloric and sulphuric acid
Environments
Thalénite-(Y) is found in granite pegmatites, associated with
fergusonite, magnetite,
fluocerite, gadolinite,
zircon, allanite,
fluorite, quartz and
microcline (HOM, Mindat). It may also occur as replacement veinlets in fluorite variety
yttrofluorite and may include
rowlandite-(Y)
and yttrialite-(Y) (Dana). Heating dehydrates it and converts it to
thortveitite
(Dana).
Localities
The type locality is Österby, St. Skedevi, Säter, Dalarna County, Sweden.
A few miles south of Kingman, Arizona, USA, thalénite occurs as a minor constituent of a single small pegmatite within an
extensive area of granite. The pegmatite is made up almost entirely of
quartz and microcline;
hematite, biotite and
zircon are present in minor amounts
(AM 71.188-193).
At the White Cloud pegmatite, Jefferson county, and the Snowfake pegmatite, Teller county, both in Colorado, USA, thalénite-(Y)
is associated with allanite
(Dana).
At the Cripple Creek mining district, Colorado, USA, thalénite-(Y) has been reported as minute crystals
in a groundmass of
phonolite
(Minrec 36-2.182).
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