Cordierite II: The role of CO2 and H2O
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B.A. Kolesov
und
C.A. Geiger
Abstract
Polarized single-crystal Raman spectra at room temperature and 5 K and polarized infrared spectra at room temperature were obtained from four natural cordierites of different compositions in the wave number region of the CO2 symmetric stretching vibration and the H2O stretching vibrations. The CO2 molecules are preferentially aligned parallel to the X axis, consistent with results from X-ray diffraction and optical studies. The CO2 contents of six natural cordierites, previously studied by powder IR methods (Vry et al. 1990), were determined via Raman spectroscopy. A linear relationship was found between CO2 content and the Raman intensity ratio of the normalized CO2 stretching mode against a Si-O stretching mode. This permits a determination of the CO2 contents in cordierite using micro-Raman measurements. The internal stretching modes between 3500 and 3800 cm-1 were assigned to various types of H2O molecules occurring in the channel cavity. Three different orientations of H2O molecules that have no interactions with alkali cations located at 0,0,0 in the sixmembered tetrahedral rings are classified in a static model as Class I H2O molecules. The H···H vector for two of them is parallel to [001], and their molecular planes lie in the XZ and YZ crystal planes. The third type has its H···H vector directed along the X axis and its molecular plane lies in the XZ plane. Two other types of H2O have interactions with the alkali cations located at 0,0,0. They are classified as Class II H2O. They distinguish themselves by the number of H2O molecules bonded to the alkali atoms. The formation of weak hydrogen bonds at low temperatures may explain the appearance of some Raman stretching modes below 200 K. The H2O molecules of Class I-Type I/II are probably dynamically disordered about [001] hopping between orientations in the XY and XZ planes down to 5 K. Class II H2O may also be disordered, but more measurements are required to describe its dynamic behavior.
© 2015 by Walter de Gruyter Berlin/Boston
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Artikel in diesem Heft
- Measurement of crystal size distributions
- Pressure dependence of the solubility of Ar and Kr in melts of the system SiO2-NaAlSi2O6
- Solubility behavior of water in haploandesitic melts at high pressure and high temperature
- Proton-containing defects at forsterite {010} tilt grain boundaries and stepped surfaces
- Incorporation of Fe3+ into forsterite and wadsleyite
- Molecular dynamics simulation of Al/Si-ordered plagioclase feldspar
- Cation ordering and structural variations with temperature in MgAl2O4 spinel: An X-ray single-crystal study
- Aluminium coordination in tektites: A XANES study
- Crystal structure of Cr-mullite
- Structure of synthetic 2-line ferrihydrite by electron nanodiffraction
- Transmission electron microscopy study of gaudefroyite, Ca8Mn6 3+[(BO3)6(CO3)2O6]
- Nano- to micro-scale decompression products in ultrahigh-pressure phengite: HRTEM and AEM study, and some petrological implications
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- The dissolution of hectorite: In-situ, real-time observations using atomic force microscopy
- Quantification of minor phases in growth kinetics experiments with powder X-ray diffraction
- Illite-smectite structural changes during metamorphism in black Cambrian Alum shales from the Baltic area
- The tremolite-actinolite-ferro–actinolite series: Systematic relationships among cell parameters, composition, optical properties, and habit, and evidence of discontinuities
- Cordierite I: The coordination of Fe2+
- Cordierite II: The role of CO2 and H2O
- Crystal chemical variations in Li- and Fe-rich micas from Pikes Peak batholith (central Colorado)
- The crystal structure of TlAlSiO4: The role of inert pairs in exclusion of Tl from silicate minerals
- The structure of agrinierite: a Sr-containing uranyl oxide hydrate mineral
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- The crystal structure of pararobertsite and its relationship to mitridatite
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