Greenish brown crystal aggregates of the extremely rare REE mineral cappelenite-(Y) from the TL in Norway (Lille Arøya, Langesundsfjorden, Larvik, Vestfold og Telemark, Norway). Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Cappelenite-(Y)
Cappelenite-(Y) is an IMA-recognized mineral species in the silicate class, with the chemical formula BaY₆B₆Si₃O₂₄F₂.
It crystallizes in the hexagonal crystal system (space group P3).
Key properties: Mohs hardness 6–6.5; specific gravity 4.407; Vitreous to greasy luster; optically uniaxial.
IMA symbol Cpp-Y, IMA status: approved, named in 1884.
Found in a small vein in nepheline syenite pegmatite.
It is found associated with WÄohlerite, rosenbuschite, thorite, catapleiite, lº avenite, nepheline, sodalite.
The name refers to D. Cappelen of Holden, Norway, a collector who discovered the mineral, and its yttrium content.