Yttrialite from Ivedal, Iveland has a chemical composition very close to the theoretical formula RE2Si2O7. Some Th and U substitutes for RE, their higher valencies being balanced by Ca, Fe2+ and Mn. X-ray data indicate the existence of three different minerals with the chemical composition RE2Si2O7: thalenite, yttrialite and a third mineral with a thortveitite structure which should have a new name. The structural type formed in a given situation is chiefly determined by small differences in chemical composition, but may also be influenced by pT conditions.
Yttrialite from Ivedal, Iveland, South Norway