Observation of the oxidation of galena using Raman spectroscopy

Oxidation of galena (PbS) to oxysulfates, (PbO·PbSO₄, 3PbO·PbSO₄ and 4PbO·PbSO₄) has been observed using Raman spectroscopy. Peaks associated with the oxidation products have been assigned. The reaction appears to be a high temperature oxidation induced by the high laser (approximately 25 mW at 514.5 nm) power density at freshly cleaved galena surfaces. Damage to the galena surface was observed visually under the microscope. Moderate laser powers (approximately 5 mW at 514.5 nm) did not result in any damage. No Raman bands were observed or expected for freshly cleaved galena because it has the rock salt structure. Laser-induced production of these oxysulfates is dramatically different from high temperature methods previously employed. This procedure will permit easy identification of galena in complex mineral ore samples. Spontaneous air oxidation of freshly cleaved galena to oxides or polysulfides was not detected.