Fluorcalciobritholite
Fluorcalciobritholite is an IMA-recognized mineral species in the silicate class, with the chemical formula (Ca,REE)₅(SiO₄,PO₄)₃F.
It crystallizes in the hexagonal crystal system (space group P6_3/m). It is a member of the Apatite structural group.
Key properties: Mohs hardness 5.5; specific gravity 4.2; White streak; Vitreous to greasy; resinous (metamict) luster; optically uniaxial.
IMA symbol Fcbri, IMA status: approved, named in 2006.
Found in veinlets cross-cutting fenitized gneiss xenoliths in foyaite (Khibiny). In alkaline metasomatite.
It is found associated with Orthoclase, nepheline, sodalite (Khibiny); fluorbritholite-(Ce), potassic feldspar, albite, alkali pyroxene, fluorapatite, natrolite (Burpala).
The prefix, calcio, indicates an analog of fluorbritholite-(Ce) with calcium dominant over rare earth elements.