H (sub 2) O and CO (sub 2) in minerals of the haueyne-sodalite group; an FTIR spectroscopy study
H (sub 2) O and CO (sub 2) in minerals of the haueyne-sodalite group; an FTIR spectroscopy study
Mineralogical Magazine (June 2009) 73 (3): 399-413
- anions
- carbon dioxide
- cell dimensions
- chemical composition
- crystal zoning
- electron probe data
- framework silicates
- FTIR spectra
- hauyne
- infrared spectra
- lattice parameters
- lazurite
- nosean
- petrography
- silicates
- single-crystal method
- sodalite
- sodalite group
- spectra
- substitution
- sulfates
- sulfides
- volatiles
- water
- X-ray diffraction data
This paper reports an infrared spectroscopic study of a set of sodalite-group minerals. The specimens have been identified using a combination of X-ray diffraction and microchemical analysis. As expected, the Si/Al ratio is approximately 1; the extra framework cation content is characterized by a well-defined Na<-->(Ca+K) substitution. The lattice parameters of the studied samples range from sodalite (sample LM11) with a=8.889(2) Aa, to hauyne (sample HR3S) with a=9.1265(2) Aa. The specimens, having the SO (super 2-) (sub 4) as a dominant anion, show a clear correlation between the a cell edge and the K content. Single-crystal FTIR spectroscopy shows that hauyne and nosean typically contain enclathrated CO (sub 2) molecules, in addition to H (sub 2) O and minor carbonate, while sodalite is virtually CO (sub 2) -free. Detailed microspectrometric mappings show a non-homogeneous distribution of volatile constituents across the crystals, which may be related to the presence of fractures in the crystals. Because of such zoning, a relatively wide variation is observed when calibrating extinction coefficients on the basis of a bulk analytical method such as CHN elemental analysis.