Crystal chemistry and thermal behavior of B-, S- and Na-bearing spurrite

• Published in: Physics and chemistry of minerals Vol. 50; no. 4; p. 33
• Main Authors: Krzhizhanovskaya, M. G., Chukanov, N. V., Mazur, A. S., Pautov, L. A., Varlamov, D. A., Bocharov, V. N.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.12.2023; Springer Nature B.V
• Subjects: Anions; Boron; Chemical composition; Crystallography and Scattering Methods; Earth and Environmental Science; Earth Sciences; Electron probes; Empirical analysis; Gas chromatography; Geochemistry; High temperature; Isomorphism; Mineral Resources; Mineralogy; NMR; NMR spectroscopy; Nuclear magnetic resonance; Original Paper; Protonation; Single crystals; Sodium; Substitutes; Sulfur; Tetrahedra; Thermal expansion; Thermodynamic properties; Triangles; X-ray diffraction; Isomorphism; Boron; Spurrite; Sulfur; Thermal stability; Crystal structure
• ISSN: 0342-1791; 1432-2021
• DOI: 10.1007/s00269-023-01257-2

Spurrite from Negra Mine, Queretaro, Mexico is characterized by a complex chemical composition. Its empirical formula derived based on electron microprobe, wet chemical analyses and gas chromatography of annealing products is H 0.18 Ca 5.01 Na 0.05 [(SiO 4 ) 1.91 (SO 4 ) 0.08 )][(CO 3 ) 0.71 (BO 3 ) 0.28 ]O 11 . The mineral was studied by single-crystal X-ray diffraction (SCXRD) as well as infrared (IR), Raman and nuclear magnetic resonance (NMR) spectroscopy. According to spectroscopic data, boron has three-fold coordination and sulfur occurs in the mineral in the sulfate form. A significant portion of carbonate groups is substituted by BO 3 3– anions. Charge compensation is achieved due to the substitution of a part of SiO 4 4– anions by SO 4 2– groups, as well as to the admixture of sodium. SCXRD shows that sodium occurs in its own site with a low occupancy. The studied sample is isotypic with the synthetic NaCa 5 (SiO 4 ) 2 (BO 3 ) compound. The IR spectrum shows possible partial protonation of the SiO 4 tetrahedra whereas bands of H 2 O molecules and isolated OH – anions are not observed. Thermal behavior of B,S,Na-bearing spurrite from Negra Mine has been studied using powder high-temperature X-ray diffraction (HTXRD) together with boron poor and S-free spurrite from Fuka Area (Japan). The studied samples are stable up to ~ 1200 °C and ~ 1100 °C, respectively, whereas synthetic B,S-free spurrite decomposes at about 900 °C. The thermal expansion is significantly anisotropic and is observed mainly in the direction perpendicular to the ac plane which is coplanar with the layers of calcium polyhedra and anionic pseudo-layers formed by (C,B)O 3 triangles and (Si,S)O 4 tetrahedra. Isomorphism and a similarity of the thermal, baric and compositional (C-B substitution) deformations of spurrite-like structures are discussed.