The crystal structure and crystal chemistry of sodalite and cancrinite groups of minerals

Abstract

<p>The crystal structures of three cancrinites, four sodalites, six helvites and tugtupite have been refined using x-ray diffraction data. The nature of the crystal structure and crystal chemistry of the cancrinites and sodalites have been elucidated, with emphasis on 1) the significance of the superstructures, 2) the space group problem, 3) the order-disorder, 4) the structural variation, and 5) the stoichiometry. Also, a geometrical structural model for sodalite ha been developed and it has the following uses: a) Allows the accurate prediction of the structures of all members of the sodalite group of minerals. b) The prediction of the chemical limits of structural stability of all materials based on the sodalite structural type. c) Permits the published thermal expansion data for sodalites to be rationalized in terms of rotation of the Al/Si-0₄ tetrahedra.</p>