Pale yellow radial crytsals of the REE mineral seidite-(Ce) from the TL in Lovozero (Lovozero Massif, Murmansk Oblast, Russian Federation). Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Seidite-(Ce)
Seidite-(Ce) is an IMA-recognized mineral species in the silicate class, with the chemical formula Na₄(Ce,Sr)₂TiSi₈O₁₈(O,OH,F)₆·5H₂O.
It crystallizes in the monoclinic crystal system (space group C2/c).
Key properties: Mohs hardness 3–4; specific gravity 2.76; Vitreous to silky, resinous or dull in some specimens luster; optically biaxial.
IMA symbol Sei-Ce, IMA status: approved, named in 1993.
Sparingly in cavernous natrolite in an ultra-agpaitic pegmatite vein.
It is found associated with Belovite, vitusite, sazhinite-(Ce), steenstrupine, manganneptunite, serandite, leucosphenite, sphalerite.
The name is derived from the locality, the Seidozer massif.