gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1968.283.036.04 The Crystal Structure of Gersdorffite (III), a Distorted and Disordered Pyrite Structure Bayliss P. School of Applied Geology University of New South Wales, Kensington, New South Wales Stephenson N. C. School of Chemistry University of New South Wales, Kensington, New South Wales 9 1968 36 283 940 947 16 11 1967 Copyright © 1968, The Mineralogical Society 1968 Summary

The crystal structure of gersdorfiite (III) has been examined with three-dimensional Weissenberg X-ray diffraction data. The unit cell is isometric with a 5·6849 ± 0·0003 Å, space group PI, and four formula units per cell. This structure has the sulphur and arsenic atoms equally distributed over the non-metal atom sites of pyrite. All atoms show significant random displacements from the ideal pyrite positions to produce triclinic symmetry, which serves to distinguish this mineral from a disordered cubic gersdorffite (II) and a partially ordered cubic gersdorffite (I). Factors responsible for the atomic distortions are discussed.