Rapidcreekite of anthropogenic origin - ’korkinoite’ from burnt mine dump in the Chelyabinsk coal basin, South Urals, Russia: crystal structure refinement, thermal behavior and spectroscopic characterization

[摘要] Anthropogenic rapidcreekite, Ca2(SO4)(CO3)·4H2O, from burnt dumps of coal mines in the Chelyabinsk coal basin, SouthUrals, Russia, previously described as 'korkinoite', has been studied by single-crystal X-ray diffraction, high-temperaturepowder X-ray diffraction, infrared (IR) and Raman spectroscopy. The mineral is orthorhombic, Pcnb, a = 15.5334(6)Å, b = 19.2379(7) Å, c = 6.1625(3) Å, V = 1841.54(13) Å3. The crystal structure is based upon heteropolyhedral sheetsparallel to (100) and can be described as produced from the crystal structure of gypsum by chemical twinning. The Ca1and Ca2 sites are coordinated by six O atoms and two H2O molecules each. The CaO8 polyhedra form chains parallel tothe с axis, connected via CO3 groups and SO4 tetrahedra to form a two-dimensional arrangement. The sheets are linkedto each other by means of the hydrogen bonding network. The main bands of the IR and Raman spectra correspond tosymmetric and asymmetric vibrations in the SO42– tetrahedra and CO32– groups. The OH– stretching region possesseshigh-intensity peaks. ’Korkinoite’ is stable up to 200 °C. Thermal expansion has a strong anisotropic character in theab and bc planes and is almost isotropic within the ac plane. The thermal expansion coefficients are approximatelythe same at room temperature and 200 °C (×10–6 °C–1): (αa = 53.7, αb = 11.6, αc = 52.0, αv = 117.3 (25 °C); αa = 53.2,αb = 11.6,αc = 51.6, αv = 116.4 (200°C)). The maximal thermal expansion is along [100] (perpendicular to the plane ofthe layers). Both 'korkinoite' (anthropogenic rapidcreekite) and rapidcreekite are structurally related to gypsum due to theunit-cell twinning induced by replacing one-half of sulfate groups in gypsum by carbonate ions in rapidcreekite. Thesestructural relations determine the similarity of thermal behavior of gypsum and rapidcreekite with strongly anisotropicexpansion within the sheet of Ca polyhedra and sulfate or sulfate and carbonate groups. The current study confirms that'korkinoite' is identical to rapidcreekite, except for the insignificant differences in the chemical composition.

[学科分类] 自动化工程

[关键词] burned coal dumps;crystal structure;thermal behavior;spectroscopic data;'korkinoite';rapidcreekite;gypsum