Crystal Structure of Macphersonite (Pb4SO4(CO3)2(OH)2): Comparison with Leadhillite

Ian M. Steele1, Joseph J. Pluth11, 2, 3 and Alec Livingstone4, 5
1 Department of Geophysical Sciences, The University of Chicago, Chicago IL 60637, USA
2 Consortium for Advanced Radiation Sources, The University of Chicago, Chicago IL 60637, USA
3 Materials Research Science and Engineering Center, The University of Chicago, Chicago IL 60637, USA
4 Department of Geology, The Royal Museum of Scotland, Chambers St., Edinburgh EH1 1JF, UK
5Present address: 6 St. Ronan's Terrace, Innerleithen, Peeblesshire EH44 6RB, Scotland

Abstract: The crystal structure of macphersonite (Pb4SO4(CO3)2(OH)2, Pcab, a = 9.242(2), b = 23.050(5), c = 10.383(2) Å) from Leadhills, Scotland has been determined to an R = 0.053. The structure has many features in common with its polymorph leadhillite including three distinct types of layers. Layer A includes sulphate tetrahedra, Layer B is composed of Pb and OH, while Layer C is composed of Pb and CO3 with topology identical to that in cerussite. In both macphersonite and leadhillite these layers are stacked along [010] as ...BABCCBABCC... The double CC layer is almost identical in the two structures and forms a structural backbone and occurs in other structures including hydrocerussite and plumbonacrite. The sulphate layer shows the greatest difference between the two structures and can be described by a pattern of up or down pointing tetrahedra. For macphersonite the sequence along [001] is ...UDUDUD... while in leadhillite the sequence along [010] is ...UDDUUDDU... This latter sequence effectively doubles b relative to the equivalent direction in macphersonite. Susannite, a third polymorph, may have yet another sequence of sulphates to give trigonal symmetry; by heating leadhillite, displacive movements of sulphate groups may occur with a conversion to susannite.

Keywords: macphersonite • leadhillite • susannite • cerussite • hydrocerussite • carbonate • sulphate

Mineralogical Magazine; August 1998 v. 62; no. 4; p. 451-459; DOI: 10.1180/002646198547828
© 1998, The Mineralogical Society
Mineralogical Society (