Brown crystal aggregates of the rare mineral illimaussite-(Ce) from the TL in Ilimaussaq (Ilímaussaq, Narsaq, Kujalleq, Greenland). Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Ilímaussite-(Ce)
Ilímaussite-(Ce) is an IMA-recognized mineral species in the silicate class, with the chemical formula (Ba,Na)₁₀K₃Na₄.₅Ce₅(Nb,Ti)₆O₆(Si₁₂O₃₆)(Si₉O₁₈)(O,OH)₂₄.
It crystallizes in the hexagonal crystal system (space group R32).
Key properties: Mohs hardness 4; specific gravity 3.6; Resinous luster; optically uniaxial.
IMA symbol Ilí-Ce, IMA status: approved, named in 1965.
Found in a hydrothermal ussingite-analcime vein cutting sodalite syenite in an alkalic massif.
It is found associated with Chkalovite, epistolite.
The name refers to the Il¶³maussaq intrusion, where it was discovered.