Yttrialite or Yttrialite-(Y) is a rare yttrium thorium sorosilicate mineral with formula: (Y,Th)₂Si₂O₇. It forms green to orange yellow masses with conchoidal fracture. It crystallizes in the monoclinic-prismatic crystal system. It has a Mohs hardness of 5 to 5.5 and a specific gravity of 4.58. It is highly radioactive due to the thorium content.

Yttrialite-(Y)
Yttrialite-(Y) found in Finland
General
Category	Sorosilicates
Formula (repeating unit)	Y2Si2O7
IMA symbol	Ytt-Y[1]
Strunz classification	9.BC.05
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	P21/m
Identification
Color	olive-green, brown to black
Other characteristics	Radioactive
References	[2][3]

It is found associated with gadolinite. It was first described in 1889 for an occurrence in the Rode Ranch pegmatite on Baringer Hill, Llano County, Texas. It has also been reported from the Suishouyama pegmatite on Honshū, Japan, and from occurrences in Norway and Sweden.