gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/002646199549005 Crystal Structure of Barstowite (3PbCl2·PbCO3-H2O) Steele I. M. 1 Pluth J. J. 1 2 3 Stanley C. J. 4 Department of Geophysical Sciences, The University of Chicago, Chicago IL 60637, USA Consortium for Advanced Radiation Sources, The University of Chicago, Chicago IL 60637, USA Materials Research Science and Engineering Center, The University of Chicago, Chicago IL 60637, USA Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK 12 1999 63 6 901 907 12 1 1999 17 3 1999 Copyright © 1999, The Mineralogical Society 1999 Abstract

The crystal structure of barstowite (3PbCl2·PbCO3·H2O, P21/m, a = 4.2023(5), b = 9.2020(7), c = 16.6608(6)(Å), β = 91.829(9)°) from Bounds Cliff, St Endellion, Cornwall, has been determined to an R = 0.036. The structure can be described in terms of three layers stacked along [001] in the sequence ...CACBCACBC... to give a 16.7 Å repeat. Layer A consists of face-sharing PbCl8 distorted square antiprisms. Layer B is composed of Pb coordinated to 5 Cl and 2 O each with two H to form H2O groups. Layer C is formed by Pb coordinated to 5 Cl and 3 O which are from CO3 groups. The H positions are deduced and are H-bonded to O from carbonates. The structural details were in agreement with previous deductions based on infrared spectra.

 Keywords barstowite phosgenite crystal structure Bounds Cliff Cornwall