Vibrational spectroscopic study of mimetite-pyromorphite solid solutions

A number of compounds of the mimetite Pb-5(AsO4)(3)Cl-pyromorphite Pb-5(PO4)(3)Cl solid solution series were synthesized at room temperature and analyzed with Raman and infrared spectroscopy. The fundamental antisymmetric stretching (v(3)) and bending (v(4)) vibrations of the mimetite-pyromorphite solid solutions occur in the regions 720-1040 cm(-1) and 400-580 cm(-1). The band originating from the v(3) and v(4) modes shifts to higher wavenumbers between mimetite and pyromorphite because the atomic mass of As is higher than P and As-O bonds are longer than P-O bonds. The position, shape and relative intensity of the bands vary primarily as a function of As/(As + P) in the analyzed solid. The strong correlations between the positions of the vibrational modes and the As/(As + P) ratio can be used to determine the composition of the investigated natural and synthetic samples of the minerals from the mimetite-pyromorphite series. (C) 2011 Elsevier Ltd. All rights reserved.