gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1969.037.287.04 Segregation and Cation-Ordering in Sjögrenite and Pyroaurite Taylor H. F. W. Department of Chemistry, University of Aberdeen, Old Aberdeen, Scotland 9 1969 37 287 338 342 30 12 1968 Copyright © 1969, The Mineralogical Society 1969 Summary

A specimen from Långban, Sweden, was found to consist largely of sjögrenite in which segregation and ordering of the metal cations had occurred, yielding an intergrowth of regions of two main types with compositions probably of or near Mg2/3Fe1/3(OH)2(CO3)1/6(H2O)0·4 and Mg12/13Fe1/13(OH)2(CO3)1/26(H2O)0·8. To a smaller extent segregation had proceeded further, giving regions probably approximating to the end-member Mg(OH)2.H2O. It is suggested that the names sjögrenite and pyroaurite be used for the 2H- and 3R- polytypes of this structure irrespective of Mg:Fe ratio, segregation, or cation ordering.