Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original Paper

Milan Novák, Jiří Sejkora, Mark A. Cooper

Cyrilovite from Cyrilov, western Moravia, Czech Republic; new data on the type material

Journal of the Czech Geological Society, volume 45 (2000), issue 1-2, 101 - 106

The type material of cyrilovite from Cyrilov was studied by the means of electron microprobe, X-ray powder diffraction and IR spectroscopy. Cyrilovite is close to the end-member composition NaFe³⁺₃ (OH)₄ (PO₄)₂. 2 H₂O with minor concentrations of Al (0.00-0.10 apfu) and Ca (0.01-0.05 apfu), insignificant substitutions Fe³⁺ → Al and CaFe²⁺ → NaFe³⁺ are indicated. The lattice parameters - a = 7.3227(3), c = 19.332(1) Å, V = 1036.61(8) ų and density D_calc = 3.112 g.cm^-3 of cyrilovite calculated from powder data are very close to those obtained from the single crystal refinement - a = 7.3255(4), c = 19.328(2) Å, V = 1037.2(2) ų and D_calc = 3.106 g.cm^-3, respectively, (Cooper et al. 2000) and to cyrilovite from other localities. The infrared absorption spectrum is very close to that of cyrilovite from Cyrilov published by Tarte et al. (1984). Two structurally nonequivalent water molecules and hydroxyls may be present in the crystal structure of cyrilovite. The number of (PO₄) vibrations may also indicate that two structurally nonequivalent (PO₄) groups are present in the crystal structure but not detected by the crystal structure analysis, possibly indicating lower symmetry.