Amarantite is triclinic, space group Pl. The lattice constants are a = 8.976Â, 6 = 11.678 Å, c = 6.698 Å, a = 95.65°, β = 90.36°, y = 97.20°. The unit cell contains two formula units. The reflection intensities were measured with a single-crystal diffractometer and accurately corrected for absorption. The determination of the crystal structure was carried out with the aid of three-dimensional Patterson and Fourier syntheses. All atoms occupy the general position 2i. The parameters were refined by the full-matrix least-squares method yielding an R value for all reflections of 5.2%. The positions of the hydrogen atoms of the water molecules have been determined by means of a final three-dimensional difference-Fourier synthesis. The structure consists of Fe coordination octahedra and sulfate tetrahedra connected to form chains parallel to the c axis, linked to each other only by hydrogen bonds. Three water molecules are located between the chains and are not connected with cations. According to the results of this investigation the chemical formula of amarantite is not 2 (FeSO4OH • 3H2O) but Fe2(S04)20 • 7H20. © 1968, Walter de Gruyter. All rights reserved.
