Vibrational spectroscopy of the basic manganese and ferric phosphate minerals : strunzite, ferrostrunzite and ferristrunzite

The Raman spectra of strunzite, ferristrunzite and ferrostrunzite have been obtained at 298 and 77K using a combination of a thermal stage and Raman microscopy. These spectra are compared with their infrared spectra. The vibrational spectra of the two minerals are different, in line with differences in crystal structure and composition. Some similarity in the Raman spectra of the hydroxyl-stretching region exists, particularly at 298 K, but characteristic differences in the OH deformation regions are observed. Significant shifts in the position of the Raman bands are observed by obtaining the spectra at 77K. Differences are also observed in the phosphate stretching and deformation regions.