Pseudosymmetry and cation ordering in heterophyllosilicates. 1. Refinement of the crystal structure of schüllerite Ba2Na(Mn,Ca)(Fe3+,Mg,Fe2+)2Ti2(Si2O7)2(O,F)4
https://doi.org/10.24930/1681-9004-2025-25-2-212-220
EDN: YVUQHF
Abstract
Research subject. Currently, the symmetry of schüllerite and the choice of space group (sp. gr.) in its structure are subjects of debate. In this work, a re-examination of the holotype sample of schüllerite was conducted.
Materials and Methods. The mineral schüllerite was found in the Löhley basalt quarry (Eifel volcanic area, Germany). The crystal structure was studied using single-crystal X-ray analysis.
Results. We refined the crystal structure of schüllerite within two space groups – acentric P1 and centrosymmetric P1 using data sets for 2496 and 1683 independent reflections with I > 3σ(I), respectively. The final R-factor values were 4.42 % in sp. gr. P1 and 4.51 % in sp. gr. P1 . The parameters of the triclinic unit cell are: a = 5.4055(3) Å, b = 7.0558(3) Å, c = 10.1945(6) Å, α = 99.838(4)°, β = 99.715(5)°, γ = 90.065(4)°, V = 377.43(4) Å3. The idealized formula is Ba2Na(Mn,Ca)(Fe3+,Mg,Fe2+)2Ti2(Si2O7)2(O,F)4.
Conclusions. The acentric space group P1 is proposed as more suitable for describing the structure of schüllerite, as it allows for the identification of more existing differences in site occupancies and cation-anion bond lengths in HOH modules.
Supporting agencies: This work supported by the Russian Science Foundation, grant No. 20-77-10065-П (X-ray structural analysis and refinement of crystal structures). The collection of material for research in the Löhley quarry and the determination of the chemical composition of schüllerite were performed in accordance with the State Assignment theme, state registration number 124013100858-3. The crystal-chemical analysis of the schüllerite structure was partially performed within the framework of the state assignment of the Kurchatov Institute National Research Center
About the Authors
G. S. Ilyin
Federal Research Center “Kola Science Center RAS”
Russian Federation
Russian Federation
Grigory S. Ilyin
184209; 10a Fersman st.; Apatity
N. V. Chukanov
Federal Research Center of Problems of Chemical Physics and Medicinal Chemistry, RAS
Russian Federation
Russian Federation
Nikita V. Chukanov
142432; 1 Academician Semenov av.; Chernogolovka
R. K. Rastsvetaeva
NRC Kurchatov Institute
Russian Federation
Russian Federation
Ramiza K. Rastsvetaeva
123182; 1 Academician Kurchatov sq.; Mosсow
S. M. Aksenov
Federal Research Center “Kola Science Center RAS”
Russian Federation
Russian Federation
Sergey M. Aksenov
184209; 10a Fersman st.; Apatity
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Review
For citations:
Ilyin G.S., Chukanov N.V., Rastsvetaeva R.K., Aksenov S.M. Pseudosymmetry and cation ordering in heterophyllosilicates. 1. Refinement of the crystal structure of schüllerite Ba2Na(Mn,Ca)(Fe3+,Mg,Fe2+)2Ti2(Si2O7)2(O,F)4. LITHOSPHERE (Russia). 2025;25(2):212-220. (In Russ.) https://doi.org/10.24930/1681-9004-2025-25-2-212-220. EDN: YVUQHF
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