Original paper

The crystal structures of lavendulan, sampleite, and a new polymorph of sampleite

Giester, Gerald; Kolitsch, Uwe; Leverett, Peter; Turner, Peter; Williams, Peter A.


The crystal structures of lavendulan from the Hilarion mine, Laurion, Greece, and isotypic sampleite from the Northparkes mine, New South Wales, Australia, have been determined from single-crystal diffraction data, resulting in a revision of the symmetry. The structure of lavendulan, NaCaCu5(AsO4)4Cl·5H2O (space group P21/n, a = 10.011(1), b = 19.478(2), c = 10.056(1) Å β = 90.37(1)°, V = 1960.8(3) Å3, Z = 4) was solved from X-ray data (MoKα, CCD area detector) and refined to R1(F) = 5.35 % for 4179 observed reflections with Fo > 4σ (Fo). The structure of sampleite, NaCaCu5(PO4)4Cl·5H2O, was determined from synchrotron data (CCD area detector) obtained from a twinned crystal (space group P21/n, a = 9.676(2), b = 19.284(4), c = 9.766(2) Å, β = 90.07(1)°, V = 1822.3(6) Å3, Z = 4) and refined to R1(F) = 4.44 % for 2601 observed reflections with Fo 4σ(Fo). The heteropolyhedral sheet in the polymorph is topologically identical to that of sampleite (and lavendulan), but the stacking of these sheets is slightly different. Thus, the polymorph may be considered a polytype if the apparently slightly reduced water content of the polymorph is neglected. Some physico-chemical properties of the sampleite polymorph are given.Sheets identical to those in lavendulan are encountered in zdenekite, the Pb-analogue of lavendulan. Very similar sheets are found in andyrobertsite, calcio-andyrobertsite(-1M), calcio-andyrobertsite-2O, richelsdorfite, and probably bleasdaleite, mahnertite, lemanskiite and the inadequately characterized, lavendulan-related species shubnikovite.


lavendulansampleitecrystal structurecrystal chemistrypolymorphism