• Vapnik, Yevgeny
• Galuskin, Evgeny V.
• Murashko, Mikhail N.
• Galuskina, Irina O.
• Krüger, Biljana

Abstract

<jats:title>Abstract</jats:title><jats:p>The new mineral khurayyimite Ca<jats:sub>7</jats:sub>Zn<jats:sub>4</jats:sub>(Si<jats:sub>2</jats:sub>O<jats:sub>7</jats:sub>)<jats:sub>2</jats:sub>(OH)<jats:sub>10</jats:sub>·4H<jats:sub>2</jats:sub>O occurs in colorless spherulitic aggregates in small cavities of altered spurrite marbles located in the northern part of the Siwaqa pyrometamorphic rock area, Central Jordan. It is a low-temperature, hydrothermal mineral and is formed at a temperature lower than 100 °C. Synchrotron single-crystal X-ray diffraction experiments have revealed that khurayyimite crystallizes in space group <jats:italic>P</jats:italic>2<jats:sub>1</jats:sub>/<jats:italic>c</jats:italic>, with unit cell parameters <jats:italic>a</jats:italic> = 11.2171(8), <jats:italic>b</jats:italic> = 9.0897(5), <jats:italic>c</jats:italic> = 14.0451(10) Å, β = 113.297(8)º, V = 1315.28(17) Å<jats:sup>3</jats:sup> and Z = 2. The crystal structure of khurayyimite exhibits tetrahedral chains of periodicity 6. The sequence of SiO<jats:sub>4</jats:sub> and ZnO<jats:sub>2</jats:sub>(OH)<jats:sub>2</jats:sub>-tetrahedra along the chain is Si–Si-Zn. The neighboring SiO<jats:sub>4</jats:sub>-tetrahedra of the corrugated chains are bridged by additional ZnO<jats:sub>2</jats:sub>(OH)<jats:sub>2</jats:sub>-tetrahedra to form 3-connected <jats:italic>dreier</jats:italic> rings. The chains can be addressed as loop-branched <jats:italic>sechser</jats:italic> single chains {<jats:bold><jats:italic>lB</jats:italic></jats:bold>, 1<jats:sup>1</jats:sup><jats:sub>∞</jats:sub>}[<jats:sup>6</jats:sup>Zn<jats:sub>4</jats:sub>Si<jats:sub>4</jats:sub>O<jats:sub>21</jats:sub>]. The chains are linked by clusters of five CaO<jats:sub>6</jats:sub> and two CaO<jats:sub>7</jats:sub> polyhedra with additional OH groups and H<jats:sub>2</jats:sub>O molecules in the coordination environment. Based on the connectedness and one-dimensional polymerisations of tetrahedra (TO<jats:sub>4</jats:sub>)<jats:sup>n−</jats:sup>, chains of khurayyimite belong to the same group as vlasovite Na<jats:sub>2</jats:sub>ZrSi<jats:sub>4</jats:sub>O<jats:sub>11</jats:sub>, since they can be described with geometrical repeat unit <jats:sup>c</jats:sup>T<jats:sub>r</jats:sub> = <jats:sup>2</jats:sup>T<jats:sub>4</jats:sub><jats:sup>3</jats:sup>T<jats:sub>4</jats:sub> and topological repeat unit <jats:sup>c</jats:sup>V<jats:sub>r</jats:sub> = <jats:sup>2</jats:sup>V<jats:sub>2</jats:sub><jats:sup>3</jats:sup>V<jats:sub>2</jats:sub>. </jats:p>

Topics

• impedance spectroscopy
• mineral
• cluster
• x-ray diffraction
• experiment
• one-dimensional
• space group