The Crystal Structure of Scorodite

Abstract

The crystal structure of scorodite was determined by means of the Laue and the rotating-crystal methods. Xyiay data obtained from oscillation photographs taken with MoKoc radiation showed the structure to be built upon a simple orthorhombic unit cell with dimensions: a=10.40kX, b=8.94kX, c=10.13kX, containing eight units of the chemical formula, FeAsO₄⋅2H₂O. All the atoms are in general positions of the space group D¹⁶_2h Pbca. The values of atomic parameters were &termined by the method of trial and error. The arsenate group has the configuration of a slightly distorted tetrahedron. Each iron atom is surrounded by four oxygen atoms, each hem four different arsenate groups, and two water molecules at the corners of a distorted octahedron, the latter occupying its adjacent corners.