Infrared spectra of Mg2Ca(SO4)(3), MgSO4, hexagonal CaSO4, and orthorhombic CaSO4

Fourier-transform infrared (IR) spectra have been obtained from 450 to 1400 cm(-1) for the sulfate ion in Mg2Ca(SO4)(3), MgSO4, and the hexagonal and orthorhombic crystalline forms of CaSO4. This appears to be the first repor t of IR spectra for Mg2Ca(SO4)(3) and hexagonal CaSO4. Except for the numbe r of satellite peaks, the spectra of Mg2Ca(SO4)(3) and hexagonal CaSO4 clos ely resemble those of MgSO4 and orthorhombic CaSO4. All of these spectra ca n be interpreted on the basis of C-2v symmetry for the anion. The cause(s) of satellite peaks are uncertain; the satellites suggest that the sulfate m ay occupy more than one position or orientation, with major:minor occupancy ratios of about 3:2. (C) 1999 Elsevier Science B.V. All rights reserved.