Cation and anion ordering and clustering in the system Lithian muscovite, Trilithionite and Polylithionite

• Applicants: Privatdozent Dr. Michael Fechtelkord; Dr. Bernd Marler
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2018 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 405948055

• Final Report Year: 2023

Final Report Abstract

A large number of lepidolites K(LixAl3-x)[Si2xAl4-2xO10](OH)yF2-y and Li-muscovites K(LixAl2-x/3□1-2x/3)[Si3AlO10](OH)yF2-y were synthesised by a gelling method in combination with hydrothermal syntheses at a pressure of 2 kbar and a temperature of 873 K. The nominal composition ranged between 0.0 ≤ x ≤ 2.0 and 0.0 ≤ y ≤ 2.0, i.e., from polylithionite K[Li2.0Al][Si4.0O10](OH)yF2-y over trilithionite K[Li1.5Al1.5][AlSi3.0O10](OH)yF2-y to muscovite K[Al2.0□][AlSi3.0O10](OH)yF2-y . 1H, 19F, 29Si, 27Al MAS NMR and 27Al MQMAS NMR spectroscopy has been performed to investigate the order/disorder state of Si and Al in the tetrahedral layers and of Li, Al, OH and F in the octahedral layer. The synthetic mica crystals are very small, ranging from 0.1 μm to 5 μm. Rietveld structure analyses on 12 samples showed that nearly all samples consist of two mica polytypes (1M and 2M1) of varying proportions. In the case of lepidolites, the 1M/2M1-ratio depends on the Li/Al ratio of the reaction mixture. The refinement of the occupancy factors of octahedral sites shows that lepidolites (1.5 ≤ x ≤ 2.0) represent a solid solution series with polylithionite and trilithionite as the endmembers. In the case of the Li-muscovites (0.0 ≤ x ≤ 1.5) the 1M/2M1-ratio depends on the amount of impurity phases like eucryptite or sanidine depleting the reaction mixture of Li or Al. There is no solid solution between trilithionite and muscovite, instead, the Li-muscovite crystals consist of domains differing in the relative proportions of muscovite and trilithionite. The overall composition of the synthesized micas which consist of two polytypes can be characterised by 29Si, 1H and 19F MAS NMR spectroscopy. The Si/Al ratio in the tetrahedral layers and thus the content of [4]Al was calculated by analysing the signal intensities of the 29Si MAS NMR experiments. The Li content xest was calculated from the measured tetrahedral Si/Al ratio of the 29Si MAS NMR signals. The calculated Li-contents xest of samples between polylithionite and trilithionite agree with the expected values. F-rich samples show slightly increased values and the OH-samples lower values. Lepidolites containing exclusively F (x = 1.5 – 2.0, y = 0.0) could be obtained, but no lepidolite with only OH (x = 1.5 - 2.0 and y = 2.0) was observed after synthesis. With decreasing Li-content, x ≤ 1.2, Li-muscovites containing mostly hydroxyl (y > 1.0) are formed. It was possible to synthesise fluorine containing micas with a Licontent as low as 0.3 and y = 0.2 - 1.8. The 19F and 1H MAS NMR experiments that F and OH are not distributed statistically but local structural preferences exist. F is attracted by Li-rich and OH by Al-rich environments.

Publications

• 1H, 19F and 29Si MAS NMR investigations of synthetic lepidolite samples with variable OH/F ratios. Acta Crystallographica Section A Foundations and Advances, 75(a2), e610-e610.
  Sulcek, Lara & Fechtelkord, Michael
  
• Changes in the cationic and anionic arrange- ments in the trilithionite – polylithionite system. Microsymposium Talk on the 27th Annual Meeting of the German Crystallographic Society (DGK), Leipzig, 25 - 28 March 2019. Zeit- schrift für Kristallographie, Supplement 39, 49. Meeting Abstract S17-01.
  Sulcek, L.; Becker, N. & Fechtelkord, M.
  
• Solid State NMR investigations of cation and anion ordering in the system Lithian muscovite – Trilithionite. Poster on the 27th Annual Meeting of the German Crystallographic Society (DGK), Leipzig, 25 - 28 March 2019. Zeit- schrift für Kristallographie, Supplement 39, 120. Meeting Abstract P111.
  Fechtelkord, M.; Becker, N. & Sulcek, L.
  
• {1H/19F} –> 29Si/27Al CPMAS and HETCOR spectroscopy of synthetic lepidolites: connectivities between F/OH and Si/Al in the octahedral and tetrahedral sheets. Acta Crystallographica Section A Foundations and Advances, 75(a2), e615-e615.
  Fechtelkord, Michael & Sulcek, Lara
  
• Solid‐state nuclear magnetic resonance investigation of synthetic phlogopite and lepidolite samples. Magnetic Resonance in Chemistry, 58(11), 1099-1108.
  Sulcek, Lara; Langner, Ramona; Werner‐Zwanziger, Ulrike; Zwanziger, Josef W.; Martineau‐Corcos, Charlotte & Fechtelkord, Michael
  
• Investigation of polymorphism in the system polylithionite - trilithionite – muscovite. Experimental Report on proposal I-20200173 beamline P08 from 22 to 24 March 2021
  Fechtelkord, M., Sulcek, L. & Marler, B.
  
• Cation and anion ordering and clustering in the system muscovite, trilithionite and polylithionite. PhD Thesis, Ruhr-Universität Bochum.
  Sulcek L.
  
• Cation and anion ordering in synthetic lepidolites and lithian muscovites: Influence of the OH/F and Li/Al ratio on the mica formation studied by NMR spectroscopy and X-ray diffraction. Poster on the 31st Annual Meeting of the German Crystallographic Society (DGK), Frankfurt a. M., 27 - 30 March 2023.
  Fechtelkord, M., Sulcek, L. & Marler, B.
  
• Cation and anion ordering in synthetic lepidolites and lithian muscovites: influence of the OH ∕ F and Li ∕ Al ratios on the mica formation studied by NMR (nuclear magnetic resonance) spectroscopy and X-ray diffraction. European Journal of Mineralogy, 35(2), 199-217.
  Sulcek, Lara; Marler, Bernd & Fechtelkord, Michael