Ca3SiO4Cl2-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[(Si0.98P0.03) Sigma(1.01)O4]Cl-2, in good agreement with its ideal formula. Ca3SiO4Cl2 is monoclinic, space group P2(1)/c, Z = 4, a = 9.8367(6) angstrom, b = 6.7159(4) angstrom, c = 10.8738(7) angstrom, beta = 105.735(6)degrees, V = 691.43(8) angstrom(3). 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 (R-1 = 0.037) and stable up to 660 degrees 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 (nu(3)), 848 ( nu(1)), 600 (nu(4)), 466 (nu(2)), 372 ( nu(2)). 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.