Ca 3 SiO 4 Cl 2 —An Anthropogenic Phase from Burnt Mine Dumps of the Chelyabinsk Coal Basin: Crystal Structure Refinement, Spectroscopic Study and Thermal Evolution.

The mineral-like phase Ca₃SiO₄Cl₂, an anthropogenic anhydrous calcium chlorine-silicate from the Chelyabinsk coal basin has been investigated using single-crystal and high-temperature powder X-ray diffraction and Raman spectroscopy. The empirical formula of this phase was calculated as Ca_2.96[(Si_0.98P_0.03)_Σ1.01O₄]Cl₂, in good agreement with its ideal formula. Ca₃SiO₄Cl₂ is monoclinic, space group P2₁/c, Z = 4, a = 9.8367(6) Å, b = 6.7159(4) Å, c = 10.8738(7) Å, β = 105.735(6)°, V = 691.43(8) ų. The crystal structure is based upon the pseudo-layers formed by Ca–O and Si–O bonds separated by Cl atoms. The pseudo-layers are parallel to the (100) plane. The crystal structure of Ca₃SiO₄Cl₂ was refined (R₁ = 0.037) and stable up to 660 °C; it expands anisotropically with the direction of the strongest thermal expansion close to parallel to the [−101] direction, which can be explained by the combination of thermal expansion and shear deformations that involves the 'gliding' of the Ca silicate layers relative to each other. The Raman spectrum of the compound contains the following bands (cm^–1): 950 (ν₃), 848 (ν₁), 600 (ν₄), 466 (ν₂), 372 (ν₂). The bands near 100–200 cm⁻¹ can be described as lattice modes. The compound had also been found under natural conditions in association with chlorellestadite. [ABSTRACT FROM AUTHOR]