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Anhydrite: Crystal structure | Sample photo | Raman spectrum | Interpretation | References

Crystal structure of Anhydrite



Crystal Data:

Crystal System: Orthorhombic - Dipyramidal

Point Group: 2/m 2/m 2/m

Cell Data:

Space Group: Amma, a = 6.991, b = 6.996, c = 6.238, Z = 4

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Density (calc.) = 2.96 and V = 305.09 Å3

Element color: Ca, S, O
Anhydrite sample

Sample no. 5536 from the "Mineralogy and Petrography Museum Grigore Cobălcescu" of "Alexandru Ioan Cuza" University, Iaşi.

Origin: Bleiberg, Carinthia - Austria.

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Raman spectrum and vibrations of Anhydrite
Element color: S, O Toggle Grid Toggle Coordinates Reverse Spectrum

Click to in the Raman spectrum. To see the vibrations click on one of them (highlight region) and it (the selected vibration) will appear on the right side of the Raman spectrum.
Below spectra are various settings, and other vibrations of anhydrite (which are not present in this spectrum).
You have the possibility to zoom in the spectrum by selecting a spectral region you need to be increased (along axis x); to zoom keep the left mouse-click continously pressed, drag (to left or to right) and release the left button. To return to the initial size spectrum, press the right click on the spectrum -> Zoom -> Reset View.

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ν2 SO4 ν4 SO4 ν1 SO4 ν3 SO4

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Interpretation of Raman spectrum of Anhydrite

Raman spectrum for anhydrite shows the ν1 mode at 1017 cm-1. The ν2 and ν3 modes of sulfate tetrahedra split in two bands: one at 419 cm-1 and 503 cm-1 and the other one at 1129 cm-1 and 1160 cm-1. The values attributed to ν4 vibration mode are at 630 cm-1 and 678 cm-1. An additional band has been observed at 235 cm-1, which was attributed to an external mode of vibration in anhydrite crystal.

The ν4 asymmetric bending mode at 609 - 612 cm-1 reported by Bhagavantam (1938) and Liu et al. (2009), has a very weak intensity and it is integrated in 630 cm-1 band. Bhagavantam also reported a frequency at 1110 cm-1. In our spectrum, this line is overlaped by the 1129 cm-1 band. The spectrum of anhydrite presents a weak band at 235 cm-1, which may be assigned to the vibrational mode of Ca-O bonding. The band at 3395 cm-1, was assigned to the water stretching mode. Most probably the water was absorbed on the mineral surface from the air.

Anhydrite Assignments
Buzgar et al., 20091 Liu et al., 2009 Bhagavantam, 1938
235 Ca-O
419 416 415 ν2 SO4
503 499 499
612 609 ν4 SO4
630 629 628
678 676 674
1017 1017 1018 ν1 SO4
1110 ν3 SO4
1129 1128 1128
1160 1159 1160
3395 νH2O

Wavenumber of the v1 vibrational Raman mode vs. atomic mass of the cations for barite group

Figure 1. Wavenumber of the ν1 vibrational Raman mode vs. atomic mass of the cations.

If we consider the Raman spectra of the barite group (barite, celestine and anglesite) and the results presented above few considerations can be made: the wavenumber increases with an increase in the force; the stretching force constant between S-O for anhydrite it is K = 6.41 md/Å (Miyake et al., 1978); the wavenumber decreases with an increase of the atomic mass of the cations (figure 1).


• The Mineralogy Database [link]

• Crystal data (.cif file) from the American Mineralogist Crystal Structure Database [link]

1BUZGAR N., BUZATU A., SANISLAV I. V. (2009) - The Raman study on certain sulfates. Analele Stiintifice ale Universitatii “Al. I. Cuza” - Iasi, Tome 55, issue 1, 5-23 [link]

• Liu, Y., Wang, A., Freeman, J. J. (2009) - Raman, MIR, and NIR spectroscopic study of calcium sulfates: gypsum, bassanite, and anhydrite. 40th Lunar and Planetary Science Conference. The Woodlans, Texas. [link]

• Bhagavantam, S. (1938) - Interpretation of Raman Spectra in Crystals: Anhydrite and Gypsum. Proceedings of the Indian Academy of Science A, 8, 345-348. [link]

• Miyake, M., Minato, I., Morikawa, H., Iwai, S. (1978) - Crystal structures and sulphate force constants of barite, celestite and anglesite. American Mineralogist, 63, 506–510. [link]