Raman Spectra of Carbonates

Calcite

    Big calcite crystal on the left showing birefringence effect. The spectrum above has a low background. Calcite has a high intensity Raman scattering as can be seen by the very small intensity of the filtered laser line at 632.8 nm compared to Raman intensity. Calcite with its 3 peaks from around 200 cm^-1 to above 1000 cm^-1 could also be used to calibrate Raman spectra wavelengths.

Aragonite

     Spectrum of another Calcium carbonate crystal structure. The stretching carbonate ion vibration at 1080 cm^-1 is common to both Calcite and Aragonite but the features around 200 cm^-1 can be used to characterize both minerals. Raman spectroscopy can thus be used to identify such close chemical compositions.