Resonance Raman Effect in Copper Carbonate Minerals Azurite and Malachite

ABSTRACT The structures of carbonate minerals, such as azurite and malachite, have been extensively studied, but some points are still unclear. This research uses Raman spectroscopy to analyze the vibrational characteristics of these minerals, focusing on the stretching modes of the carbonate anion. The results show an unexpected intensification of the asymmetric stretching mode compared to the symmetric one, suggesting a possible resonance Raman effect influenced by Albrecht's second term. Azurite exhibited a de‐enhancement of some vibrational modes, indicating an unusual antiresonance effect, probably due to Cu(II) ions and d–d electronic transitions. Electronic spectra revealed distinct electronic transitions, with maxima at 538 nm for malachite and 466 nm for azurite. The arrangement of copper centers may deform the carbonate anion, impacting both off‐resonance and resonance effects. This study provides insights into the vibrational properties of these minerals and suggests the need for further investigations.