R2: Crystal structure, crystal chemistry, physical properties of minerals, crystal growth and applied mineralogy

[R2-07] Si-Al distribution & hydrogen bonding in ussingite (Na₂AlSi₃O₈OH): Unraveled by multi-nuclear NMR and first-principles calculation

*Xianyu Xue¹ (1. Okayama Univ., IPM)

Keywords:ussingite, Si-Al disorder, hydrogen bonding, NMR, first-principles calculation

Ussingite (Na₂AlSi₃O₈OH) is a mineral with a unique partially interrupted framework structure, containing four tetrahedral sites (T1, T2: Q⁴, T3, T4: Q³) and OH with strong hydrogen bonding. In the ordered structure, T1 is occupied by Al, and T2-T4 sites occupied by Si, but it was controversial whether Al-Si disorder exists. Here, I unambiguously demonstrated via multi-nuclear NMR and first-principles calculation that about 3.5% Si-Al disorder exists between T1 & T2 sites, which results in some of the OH having stronger and weaker hydrogen bonding than that of the ordered structure.