Pb2(AsO2OH)Cl2, a new phase from the Lavrion ancient slags, Greece: occurrence and characterization

Abstract

AbstractTransparent prismatic crystals of Pb2(AsO2OH)Cl2were collected in black metallurgical slag on the coast in the Punta Zeza area, 3 km south of the town of Lavrion, Greece. Analyses by energy-dispersive X-ray spectrometry (EDS) provided the following chemical composition: PbO 73.04, As2O315.97, Cl 11.42, O=Cl –2.58, total 97.85 wt.%. The empirical formula calculated on the basis of As = 1 is HxPb2.03(AsO3)1.00Cl1.995(x = 0.96). The infrared spectrum of Pb2(AsO2OH)Cl2has characteristic AsO33–bands at 707 and 594 cm–1, O–H stretching vibrations at 3310 and 2900 cm–1and a band at 1107 cm–1which is assigned to As–O–H bending vibrations. The structure, which is monoclinic P21/m, a = 6.4235(8), b = 5.5399(7), c = 9.321(1) Å, β = 90.767(2)°, V = 331.67(7) Å3, R1= 0.035, is identical to that of synthetic Pb2(AsO2OH)Cl2and contains two symmetrically unique Pb sites and one As site. The crystal structure is based on [Pb2AsO2OH]2+double chains interconnected via weak Pb–Cl bonds to produce a three-dimensional framework which is closely related to that of Pb oxysalt minerals containing [O2Pb3]2+chains of oxocentred [OPb4]6+tetrahedra including mendipite, damaraite, rickturnerite and plumboselite.