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

Crystal structure of Dolomite

Formula:

CaMg(CO3)2

Crystal Data:

Crystal System: Trigonal - Rhombohedral

Point Group: 3

Cell Data:

Space Group: R 3, a = 4.842, c = 15.95, Z = 3

Using the mouse (click here for more information)

Density (calc.) = 2.711 and V = 367.78 Å3

Element color: Ca, Mg, C, O
Dolomite sample
Dolomite

Sample no. 5451 from the "Mineralogy and Petrography Museum Grigore Cobălcescu" of "Alexandru Ioan Cuza" University, Iaşi.

Origin: Fiesch - Switzerland.




Click image to enlarge

Raman spectrum and vibrations of Dolomite
Element color: C, 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 dolomite (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.

Model type:
Sticks Ball-and-Sticks (1) Ball-and-Sticks (2) CPK (Spacefill)

Orientation:
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CO3 polyhedra on CO3 polyhedra off
Vibrations:
714 cm-1 - ν4b (E') 1087 cm-1 - ν1 (A'1)

Vibration on Vibration off
Download spectrum:
Raman spectrum .txt Raman spectrum .spc


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Interpretation of Raman spectrum of Dolomite

In this study only ν1 (1087 cm-1), ν4 (714 cm-1) bands are observed in the Raman spectrum, ν2 and ν3 modes are absent. The external vibration mode observed at 285 cm-1 are due to the relative translations between the cation and anionic groups (Gunasekaran, 2006).


Buzgar et al., 20091 Gunasekaran et al., 2006 Huang et al., 1960 Assignment
187 179 T(Ca, Mg, CO3)
285 309 304 T(Ca, Mg, CO3)
714 733 725 ν4 symmetric CO3 deformation
ν2 asymmetric CO3 deformation
1087 1106 1100 ν1 symmetric CO3 stretching
NO 1450 1445 ν3 asymmetric CO3 stretching
NO 1765 ν1 + v4
NO = not observed

The difference in site symmetries for dolomite and calcite results from substitution of Mg atom for one of the two Ca atoms for about each molecular oxygen atom. Thus the IR and Raman spectra of dolomite resemble those of calcite. In literature, Gunasekaran et al. (2006) and Huang et al. (1960) have reported bands for the ν3 vibrational modes of CO3 group (1450, respectively 1445 cm-1), values that in this study were not observed. Also, Gunasekaran has reported a band at 1765 cm-1 assigned to ν1 + ν4 combination.

References

• The Mineralogy Database [link]

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

1BUZGAR N., APOPEI A. I. (2009) - The Raman study on certain carbonates. Analele Stiintifice ale Universitatii “Al. I. Cuza” - Iasi, Tome 55, issue 2, 97-112 [link]

• GUNASEKARAN S., ANBALAGAN G., PANDI S. (2006) - Raman and infrared spectra of carbonates of calcite structure. Journal of Raman Spectroscopy, 37, p. 892-899 [link]