Raman spectroscopy of halogen‐containing carbonates

Raman spectroscopy complemented 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 CO 3 2− symmetric stretching vibration varies with the mineral composition. An additional band for northupite at 1107 cm −1 is observed. Raman spectra of bastnasite, parisite and northupite show single bands at 1433, 1420 and 1554 cm −1 , respectively, assigned to the ν 3 (CO 3 ) 2− asymmetric stretching mode. The observation of additional Raman bands for the ν 3 modes for some halogenated carbonates is significant in that it shows distortion of the CaO 6 octahedron. No ν 2 Raman bending modes are observed for these minerals. The band is observed in the infrared spectra, and multiple ν 2 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 forthe carbonate ν 4 in‐phase bending modes at 722 cm −1 for bastnasite, 736 and 684 cm −1 for parisite and 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.