Isomorphic substitution in vanadinite [Pb5(VO4)3Cl] : a Raman spectroscopic study

The Raman and infrared spectra of vanadinite [Pb₅(VO₄)₃Cl] specimens from three localities were studied. Raman spectra were found to be both orientation and temperature dependent. Measurement of the Raman spectra at liquid nitrogen temperature allowed better band separation and increased the intensities of weak bands, thus permitting band assignment. Two types of isomorphous substitution were identified: (a) substitution in the bulk of the crystal where electron beam microanalysis identifies the presence of calcium and copper and (b) surface substitution where infrared spectroscopy shows the isomorphous substitution of vanadate by phosphate and of chloride by hydroxyl groups.