High Quality Content by WIKIPEDIA articles! 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.