Minerals from Macedonia. V. Characterization of gypsum, barite, and their synthetic analogues by FTIR and Raman spectroscopy

The Fourier transform infrared (FTIR) and Raman spectra of gypsum (CaSO4.2H2O) and barite (BaSO4) from various localities in Macedonia were studied. Contrary to the group-theoretical predictions, it was found that the band originating from the ν2 sulfate mode (expected at around 450 cm-1) does not appear in the infrared spectra of either gypsum or barite, apparently due to the high effective symmetry of the force field for this mode. The infrared and Raman spectra of natural gypsum and its synthetic analogue are very similar. On the other hand, slight frequency differences (especially pronounced in the region of the ν3 sulfate modes) were registered in the infrared spectrum (and, to a considerably lesser extent in the Raman spectrum as well) of synthetic BaSO4 when compared to the spectrum of mineral barite. Also studied were the FTIR and Raman spectra of a mineral previously characterized as anhydrite. Although its morphological characteristics (shape, color and transparency) were quite different from those of gypsum it was shown that the studied mineral is in fact gypsum. (Original)