The Crystal Structure of Manganotychite, Na6Mn2(CO3)4(SO4), and Structural Relations in the Northupite Group

The crystal structure of manganotychite has been refined using the holotype specimen from Alluaiv Mountain, Lovozero massif, Kola peninsula, Russia. mineral is cubic, Fd3¯, a = 14.0015(3) Å, V 2744.88(18) Å3, Z 8, R1 0.020 for 388 independently observed reflections. Manganotychite isotypic to tychite and ferrotychite. Its based upon three-dimensional infinite framework formed by condensation MnO6 octahedra CO3 groups sharing common O atoms. sulfate Na+ cations reside in cavities octahedral-triangular metal-carbonate framework. In terms symmetry basic construction framework, identical that northupite, Na3Mg(CO3)2Cl. transition northupite → can be described as result multiatomic 2Cl− (SO4)2− substitution, where both chlorine ions are extra-framework constituents. However, positions occupied correspond different octahedral within skeletons Na considered an interpenetration two frameworks: anionic [Mg(CO3)2]2− cationic [ClNa3]2− with antipyrochlore topology. Both types modification diamond (or dia net) via following steps: (i) replacement vertex net M4 tetrahedron (no reduction); (ii) attachment (CO3) triangles triangular faces tetrahedra (accompanied Fd3¯m Fd3¯ (iii) filling voids resulting (iv) skeleton either (in tychite-type structures) or atoms northupite). As result, information-based structural complexity exceeds net.