Cordierite I: The coordination of Fe2+
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Charles A. Geiger
,
Thomas Armbruster
Abstract
The incorporation of Fe2+ was investigated in four natural cordierite samples. 57Fe Mössbauer, single-crystal UV-VIS optical absorption, and X-ray absorption spectroscopies, as well as X-ray single-crystal diffraction were used. Mössbauer, optical, and XAS spectroscopy show that Fe2+ is incorporated on two different structural sites in two Mg-rich samples. Mössbauer measurements give the best quantitative measure of the amounts of Fe2+, but the optical spectra are the most sensitive for determinations at low concentrations and at high-bulk Fe2+ concentrations in cordierite. The spectroscopic data are most consistent with small amounts of Fe2+ (i.e., 0.02 of Fe2+ per formula unit) being located on a tetrahedral site rather than in the center (or off center) of the six-membered tetrahedral rings or in channel cavities. X-ray single-crystal refinements on two Mg-rich cordierites show a very small excess electron density on T11 and not in the channels. A third refinement on a slightly more iron-rich sample shows, in contrast, no excess electron density on T11. We interpret these data as indicating that small amounts of Fe2+ (0.01 to 0.02 atoms per formula unit) replace tetrahedral Al11 in cordierite, where charge balance is achieved by placing Na in the center of the six-membered rings. This substitution is consistent with the known chemistry of natural cordierites and with simple structural energetics. The identification and assignment of small amounts of Fe2+ on T11 requires spectroscopic determination or careful X-ray single-crystal refinements and cannot be achieved from composition data and structural formula calculations.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- 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
- New insights into the mechanism for chloritization of biotite using polytype analysis
- 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
- The crystal structure of namibite, Cu(BiO)2VO4(OH), and revision of its symmetry
- The crystal structure of pararobertsite and its relationship to mitridatite
- Description and crystal structure of cabalzarite Ca(Mg,Al,Fe)2(AsO4)2(H2O,OH)2, a new mineral of the tsumcorite group
- Tegengrenite, a new, rhombohedral spinel-related Sb mineral from the Jakobsberg Fe-Mn deposit, Värmland, Sweden
