The Crystal Structures of Sjögrenite and Pyroaurite

L. Ingram1 and H. F. W. Taylor
Department of Chemistry, University of Aberdeen
1Née Hardman.

Summary: The crystal structures of sjögrenite and pyroaurite, two stacking modifications of approximate composition Mg6Fe2(OH)16(CO3).4H2O, have been determined by X-ray diffraction using three-dimensional methods. Sjögrenite is hexagonal, with a 3·13, c 15·66 Å, space group P63/mmc , Z = ¼; pyroaurite is rhombohedral, with aH 3·13, cH 23·49 Å, space group R3¯m or R3m, Z = ⅜. Both structures are based on brucite-like layers, with magnesium and iron distributed among the octahedral positions. The cations appear to be largely disordered, although ordered regions may occur in some crystals. Between the brucite-like layers are the water molecules and carbonate groups. These are statistically arranged, with their oxygen atoms distributed among a larger number of possible sites.

Mineralogical Magazine; December 1967 v. 36; no. 280; p. 465-479; DOI: 10.1180/minmag.1967.036.280.01
© 1967, The Mineralogical Society
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