CO (sub 2) in minerals of the cancrinite-sodalite group; pitiglianoite
CO (sub 2) in minerals of the cancrinite-sodalite group; pitiglianoite (in Micro- and mesoporous mineral phases, S. Merlino (editor))
European Journal of Mineralogy (December 2005) 17 (6): 847-851
This paper presents spectroscopic evidence for the presence of CO (sub 2) molecules within the structural channels of a member of the cancrinite-sodalite group of feldspathoids. The study was carried out using single-crystal micro-FTIR spectroscopy on a sample of pitiglianoite from Monte Cavalluccio (Bonaccorsi & Orlandi, 1996). A sharp and prominent band is observed in the medium-infrared range at 2351 cm (super -1) , which can be assigned to carbon dioxide molecules in the studied sample. Polarized-light FTIR spectra collected on a 112-mu m-thick  section show maximum absorption with E (perpendicular to) c, suggesting that the linear CO (sub 2) molecules are oriented perpendicular to the crystallographic c axis, as in beryl (Wood & Nassau, 1967) or cordierite (Armbruster & Bloss, 1980). In situ high-T FTIR data collection up to 550 degrees C shows that the CO (sub 2) band decreases in intensity and broadens with increasing T; release of carbon dioxide from the structure starts at T > 250 degrees C and is complete at approximately 450 degrees C. The same kind of behaviour is observed for structural H (sub 2) O; upon heating pitiglianoite becomes virtually anhydrous at T approximately 500 degrees C. These data suggest that the extraframework volatile composition of cancrinite-type minerals is strongly T dependent, hence the analysis of pitiglianoite may provide geothermometric information on the genetic environment (typically late-stage volcanic) of these minerals.