Munich Show 2011/10/30: a nice thalénite-(Y) crystal embedded in hosting REE-enriched granitic pegmatite; specimen ca. 8 x 7 x 7cm; diameter/length of crystal ca. 1.8 cm. From: Hundholmen, Tysfjord, Nordland, Norway. — Photo: Christian Brand · CC0
Thalénite-(Y)
Thalénite-(Y) is an IMA-recognized mineral species in the silicate class, with the chemical formula Y₃Si₃O₁₀F.
It crystallizes in the monoclinic crystal system (space group P2_1/n).
Key properties: Mohs hardness 6–6.5; specific gravity 4.16–4.41; Greasy luster; optically biaxial.
IMA symbol Tlé-Y, IMA status: approved, named in 1898.
Found in granite pegmatites.
It is found associated with Fluocerite, fergusonite, gadolinite, zircon, magnetite, allanite, fluorite, quartz, microcline. Ä.
The name refers to Professor Tobias Robert Thal¶en (1827–1905), Swedish physicist, and its high yttrium content.