Raman spectroscopy of the phase-related basic copper arsenate minerals olivenite, cornwallite, cornubite and clinoclase

Abstract

The Raman spectra of olivenite, cornwallite and its diamorph cornubite and clinoclase have been obtained at 298 and 77K using a combination of a thermal stage and Raman microscopy. The vibrational spectra of minerals are different, in line with differences in crystal structure and composition. Some similarity in the Raman spectra of the hydroxyl-stretching region exists, particularly at 298 K. Two hydroxyl-stretching frequencies are observed for each mineral with the bands for clinoclase being well separated. Characteristic differences in the OH deformation regions are observed. Differences are also observed in the arsenate stretching and deformation regions. The OAsO bending modes are identified.
The application of Raman microscopy to the study of closely related mineral phases has enabled their molecular characterisation using their Raman spectrum, thus enabling the rapid identification of phases in complex mixtures of secondary copper arsenates from the oxidized zones of base metal ore bodies.