Raman spectroscopy of halogen-containing carbonates

Abstract

Raman spectroscopy complimented with infrared spectroscopy has been used to study a series of selected natural halogenated carbonates from different origins including bastnasite, parisite and northupite. The position of CO32- symmetric stretching vibration varies with mineral composition. An additional band for northupite at 1107 cm-1 is observed. Raman spectra of bastnasite, parisite and northupite show a single band at 1433, 1420 and 1554 cm-1 respectively, assigned to the ν3 (CO3)2- asymmetric stretching mode. The observation of additional Raman bands for the ν3 modes for some halogentaed carbonates is significant in that it shows distortion of the CaO6 octahedron No ν2 Raman bending modes are observed for these minerals. The band is observed in the infrared spectra and multiple ν2 modes at 844 and 867 cm-1 are observed for parisite. A single intense infrared band is found at 879 cm-1 for northupite. Raman bands are observed for the carbonate ν4 in phase bending modes at 722 cm-1 for bastnasite, 736 and 684 cm-1 for parisite, 714 cm-1 for northupite. Multiple bands are observed in the OH stretching region for selected bastansites and parisites indicating the presence of water and OH units in the mineral structure. The presence of such bands brings into question the actual formula of these halogenated carbonate minerals.