Thalénite-(Y)

minerals

fergusonite

fluocerite

gadolinite

Formula: Y3Si3O10F
Sorosilicate (Si2O7 groups)
Specific gravity: 4.2
Hardness: 6
Streak: White
Colour: Flesh-pink, brown or greenish
Solubility: Soluble in hydrochloric and sulphuric acid
Environments

Pegmatites

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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