Brown crystals of the very rare disprosium-erbium mineral yftisite-(Y) associated to white keiviite-(Y) from the famous locality of Ytterby (Ytterby, Resarö, Vaxholm, Stockholm County, Sweden) known for the discovery of four rare earth chemical elements(Y, Er, Tb, Yb). Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Keiviite-(Y)
Keiviite-(Y) is an IMA-recognized mineral species in the silicate class, with the chemical formula Y₂Si₂O₇.
It crystallizes in the monoclinic crystal system (space group C2/m). It is a member of the Thortveitite structural group.
Key properties: Mohs hardness 4–5; specific gravity 4.45; White streak; Vitreous luster; optically biaxial.
IMA symbol Kvi-Y, IMA status: approved, named in 1984.
Found in fissures in quartz and fluorite in \amazonite" pegmatites.
It is found associated with Keiviite-(Yb), thalenite, xenotime, bastnÄasite, kuliokite-(Y), quartz, fluorite.
The name refers to the relation to keiviite-(Yb) and the yttrium content.