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

Crystal structure of Calcite

Formula:

CaCO3

Crystal Data:

Crystal System: Trigonal - Hexagonal Scalenohedral

Point Group: 3 2/m

Cell Data:

Space Group: R 3c, a = 4.989, c = 17.062, Z = 6

Using the mouse (click here for more information)

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

Element color: Ca, C, O
Calcite samples (no. 5413 and brown calcite)
CalciteCalcite Calcite

Sample no. 5413 from the "Mineralogy and Petrography Museum Grigore Cobălcescu" of "Alexandru Ioan Cuza" University, Iaşi.

Origin: Guanajuato - Mexic.


Click image to enlarge

Raman spectrum and vibrations of Calcite (no. 5413)
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 calcite (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:
715 cm-1 - ν4b (E') 1087 cm-1 - ν1 (A'1) 1437 cm-1 - ν3a (E')

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Download spectrum:
Raman spectrum .txt Raman spectrum .spc


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Raman spectrum of brown Calcite
Toggle Grid Toggle Coordinates Reverse Spectrum Download spectrum:
Raman spectrum .txt Raman spectrum .spc
Interpretation of Raman spectrum of Calcite

The intense band (ν1) of calcite spectrum corresponds to the symmetric stretching of CO3 group at 1087 cm-1. The ν2 (asymmetric deformation) vibration mode is not active in Raman. The values attributed to ν3 (asymmetric stretching) mode are 1437 cm-1 and ν4 (symmetric deformation) mode at 715 cm-1. Symmetric deformation or symmetric bending, also applies to asymmetric deformation.

The observed vibrational bands of calcite compared with well-documented values are listed below. The minor shift in positions may be due to the effects of natural impurities present in the sample.


Buzgar et al., 20091 Gunasekaran et al., 2006 Free CO32- Assignment
89 R(CO3)
162 T(Ca, CO3)
285 288 T(Ca, CO3)
715 716 680 ν4 symmetric CO3 deformation
879 ν2 asymmetric CO3 deformation
1087 1092 1063 ν1 symmetric CO3 stretching
1437 1437 1415 ν3 asymmetric CO3 stretching
1749 1754 ν1 + ν4

The lower wavenumbers of calcite (285 cm-1) observed in the above table, arise from the external vibration of the CO3 group that involve translatory oscillations of the group (relative translations between the cation and anionic group). In this spectrum are no values below 200 cm-1 because the spectral range is between 200 - 3400 cm-1.

A weak line observed at 1749 cm-1 may be regarded as the combination band of ν1 + ν4 (Gunasekaran et al., 2006). This interpretation is also favoured by Schaefer et al. However and Krishnan assigned this band to 2ν2.

The positions of the observed Raman bands are in agreement with those reported by Gunasekaran et al., 2006.

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]