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

Crystal structure of Siderite

Formula:

Fe2+CO3

Crystal Data:

Crystal System: Trigonal - Hexagonal Scalenohedral

Point Group: 3 2/m

Cell Data:

Space Group: R 3c, a = 4.72, c = 15.46, Z = 6

Using the mouse (click here for more information)

Density (calc.) = 3.87 and V = 298.28 Å3

Element color: Fe, C, O
Siderite sample
Siderite

Sample no. 5455 from the "Mineralogy and Petrography Museum Grigore Cobălcescu" of "Alexandru Ioan Cuza" University, Iaşi.

Origin: Lobenstein - Germany.




Click image to enlarge

Raman spectrum and vibrations of Siderite
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 siderite (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)

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CO3 polyhedra on CO3 polyhedra off
Vibrations:
737 cm-1 - ν4b (E') 1087 cm-1 - ν1 (A'1) 1442 cm-1 - ν3a (E')

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Download spectrum:
Raman spectrum .txt Raman spectrum .spc


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Interpretation of Raman spectrum of Siderite

The Raman spectrum of siderite is characterized by the same band of calcite at 1087 cm-1 corresponding to the symmetric stretching of CO3 group. The band at 737 cm-1 corresponds to the ν4 (O-C-O in-plane bending) vibrational mode and 1442 cm-1 to ν3 mode.

The observed vibrational bands of siderite 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 Beny, 1991 Free CO32- Assignment
R(CO3)
190 T(Fe, CO3)
289 294 T(Fe, CO3)
514 506 Fe-O
737 731
742
680 ν4 symmetric CO3 deformation
879 ν2 asymmetric CO3 deformation
1087 1087 1063 ν1 symmetric CO3 stretching
1442 1415 ν3 asymmetric CO3 stretching
1729 1726
1733
ν1 + ν4

The lower wavenumbers of siderite (289 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 1729 cm-1 may be regarded as the combination band of ν1 + ν4. This interpretation is also favoured by Schaefer et al. However and Krishnan assigned this band to 2ν2. The spectrum also presents a band at 514 cm-1, wich may be assigned to the vibration of a Fe-O bond.

The positions of the observed Raman bands are in agreement with those reported by Beny C., 1991.

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]

• BENY C. (1991) - Societe Francaise de Mineralogie et de Cristallographie - Base donnees de spectres Raman. Siderite [link]