Gypsum Spectrum

NIR Spectra of gypsum mono-crystals. Absorbance scale is standardized to 1 mm thickness. The spectrum of liquid water has been added for comparison. The different absorptions in the NIR region are due to harmonics of the vibrations of water molecule in the gypsum. The low symmetry environment of the H2O molecule in gypsum splits the spectrum in several transitions and produces the strong pleochroism observed. The fundamentals of these vibrations have been measured by Raman spectroscopy.