Gypsum Raman spectra

Fjg, 9. Satellites near the O—H valency band in the Raman spectrum of gypsum crystal... 

Figure 1-17. Sabkha surface crust with gypsum and halite crystals, Rhub-al-Khalil, Arabian desert cyanobacterial colonisation at interface with subsurface dolomitized calcite. The Raman spectrum shows the presence of scytonemin and carotene in the biological zone...

The IR spectrum obtained from a very small amount of powder detached from the piece is shown in Fig. 10. The spectrum consists mainly of gypsum substrate and no evidence for pigments is seen because our FTIR spectrometer range is at the limit of the hematite band positions. The same fitting analysis allows the identification of a small contribution of calcite, which cannot be seen in the Raman spectrum. 

Figure 9 Micro Raman spectrum of a red pigment from Convento de la Peregrina, Sahagun. (a) Synthesized spectrum after the fitting of the stored components of lime wash and black lamp (b) synthesized spectrum after the fitting of the stored components of gypsum (c) synthesized spectrum after the fitting of the stored components of hematite. The addition of parts (a), (b), and (c) matches exactly the obtained raw spectrum.

Figure 1-11. Antarctic endolith in gypsum, with Raman spectra of, upper spectrum, the surface (gypsum) and lower spectrum, the underlying cyanobacterial zone (scytonemin). The chemical structure of scytonemin is also given here...

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