The Siderite Raman spectrum and its interpretation are presented below.
Siderite sample data
|Description:||Siderite mineral sample|
|Source:||Grigore Cobălcescu Museum|
|Locality:||Lobenstein – Germany|
|Owner:||Department of Geology – Alexandru Ioan Cuza University of Iasi|
Siderite sample image
Main Raman bands of Siderite
|Wavenumbers (cm-1):||1087vs, 737w, 289m|
|Instrument settings:||Raman spectrograph HE 532nm (Horiba Jobin-Yvon)|
|Spectral resolution:||2 cm-1|
|Conditions of measurement:||at room temperature|
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 and Apopei, 2009||Beny, 1991||Free CO32-||Assignment|
|680||ν4 symmetric CO3 deformation|
|879||ν2 asymmetric CO3 deformation|
|1087||1087||1063||ν1 symmetric CO3 stretching|
|1442||1415||ν3 asymmetric CO3 stretching|
|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. 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, 1991.