Original paper

Synthesis of Pb-zoisite and Pb-lawsonite

Dörsam, Guido; Liebscher, Axel; Wunder, Bernd; Franz, Gerhard; Gottschalk, Matthias

Abstract

Hydrothermal syntheses of Pb-zoisite Pb2Al3[SiO4|Si2O7|O|OH] and Pb-lawsonite PbAl2[Si2O7|(OH)2]·H2O were performed at high pressure and temperature conditions with standard piston cylinder press experiments. Starting materials were mixtures of PbAl2O4, SiO2, PbO and H2O. The run products were characterized by single-crystal and powder X-ray diffraction, scanning electron microscopy and electron microprobe analyses.Idiomorphic colourless Pb-zoisite crystals with sizes of 60 × 50 × 120 μm were obtained at 2 GPa and 600 °C, together with Pb-lawsonite and traces of Pb-margarite and plumbotsumite Pb5Si4O8(OH)10. Single-crystal diffraction studies and structure solution of Pb-zoisite yielded space group Pnma (62), Z = 4, a = 16.4529(7) Å, b = 5.6432(2) Å, c = 10.3631(5) Å, V = 962.18 Å3, R1 = 0.067. Pb-lawsonite was obtained at 3 GPa/600 °C and at 2 GPa/400 °C. Powder-XRD pattern of Pb-lawsonite shows an orthorhombic unit cell. Peaks at (101), (103), (121), (211), (212), (213), (231), (301), (233) suggest space group Pbnm (62) with Z = 4, a = c 5.85 Å, b = 9.03 Å, c = 13.31 Å, V = 703 Å3, instead of space group Cmcn for Ca-lawsonite and P21/m for Sr-lawsonite. Group-subgroup relations of the lawsonite structure family are presented.

Keywords

lead silicatespb-margariteplumbotsumiteexperimental mineralogy