:Black yttrialite-(Y) with brown lustrous formanite-(Y) and brown britholite-(Y) with dull lustre. Locality: Lövböle, Kemiö Island, Southwestern Finland Region, Finland — Photo: Jyrki Autio · CC0
Britholite-(Y)
Britholite-(Y) is an IMA-recognized mineral species in the silicate class, with the chemical formula (Y,Ca)₅(SiO₄)₃(OH).
It crystallizes in the monoclinic crystal system (space group P2_1). It is a member of the Apatite structural group.
Key properties: Mohs hardness 6; specific gravity 4.35; Faint brown streak; Resinous to dull luster; optically uniaxial.
IMA symbol Bri-Y, IMA status: approved, named in 1938.
Found in pegmatites.
It is found associated with Yttrialite, thorogummite, tengerite, allanite.
The name refers to its chemical relation to britholite-(Ce) and dominant yttrium in its composition.