The iron oxidation state of garnet by electron microprobe: Its determination with the flank method combined with major-element analysis
-
Heidi E. Höfer
and
Gerhard P. Brey
Abstract
We have established a method to determine the oxidation state of Fe using the electron microprobe “the flank method.” This method has the possibility to analyze simultaneously the majorelement chemistry on the same spot. The method is based on FeL X-ray emission spectra that show a concomitant change of both the intensity and the wavelength of the soft FeLα and FeLβ emission lines. The method has been developed for garnets using well-characterized synthetic samples, and an empirical correction scheme has been established for self-absorption of the FeL X-ray emission. This enables the unambiguous correlation of measured intensity ratios of FeLα/FeLβ X-ray emission to the oxidation state in garnet. The flank method can be used with routine microprobe settings (e.g., 15 kV, 60 nA) and, for garnets, with minimum beam size. This way, Fe3+/ΣFe and major and trace elements can be determined within 10 minutes on the microscale. The resulting accuracy of Fe3+/ΣFe is then ±0.04 for garnets at 10 wt% total Fe. Application to natural garnet megacrysts with 8 wt% total Fe and Fe3+ known from Mössbauer spectroscopy yields excellent agreement between the two methods. For practical application, the calibration can be achieved by using three natural standards and fitting the data to Fe2+ and Fe3+ with linear equations. Through repeated measurements on homogeneous samples, the error in Fe3+/ΣFe becomes approximately ±0.02 (1σ). Optimization of analytical parameters such as beam current, measurement time, and repetition of analyses, will further lower the uncertainty.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
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- Crystallographic texture and microstructure of terebratulide brachiopod shell calcite: An optimized materials design with hierarchical architecture
- High-temperature phase relations and topological constraints in the quaternary system MgO-Al2O3-SiO2-Cr2O3: An experimental study
- Tilt and buckling modes, and acoustic anisotropy in layers with post-perovskite connectivity
- Optical absorption study of natural garnets of almandine-skiagite composition showing intervalence Fe2+ + Fe3+ → Fe3+ + Fe2+ charge-transfer transition
- Deriving formation constants for aqueous metal complexes from XANES spectra: Zn2+ and Fe2+ chloride complexes in hypersaline solutions
- Birnessite polytype systematics and identiÞ cation by powder X-ray diffraction
- Improved measurement of fission-track annealing in apatite using c-axis projection
- Improved modeling of fission-track annealing in apatite
- Intercalibration of FTIR and SIMS for hydrogen measurements in glasses and nominally anhydrous minerals
- Order and miscibility in the otavite–magnesite solid solution
- An infrared investigation of the otavite-magnesite solid solution
- Partitioning of calcium, magnesium, and transition metals between olivine and melt governed by the structure of the silicate melt at ambient pressure
- The geometric effects of VFe2+ for VMg substitution on the crystal structures of the grandidierite-ominelite series
- The iron oxidation state of garnet by electron microprobe: Its determination with the flank method combined with major-element analysis
- Gram-Charlier development of the atomic displacement factors into mineral structures: The case of samsonite, Ag4MnSb2S6
- Superstructure of Challis mordenite with doubled monoclinic unit cell
- Biopyribole evolution during tremolite synthesis from dolomite and quartz in CO2-H2O fluid
- The evolution of diamond morphology in the process of dissolution: Experimental data
- The pearceite-polybasite group of minerals: Crystal chemistry and new nomenclature rules
- Determination of layer stacking microstructures and intralayer transition of illite polytypes by high-resolution transmission electron microscopy (HRTEM)
- Structural behavior of Al3+ in peralkaline, metaluminous, and peraluminous silicate melts and glasses at ambient pressure
- The crystal structure of ingersonite, Ca3Mn2+Sb45+O14, and its relationships with pyrochlore
- Chemical composition, statistical analysis of the unit cell, and electrostatic modeling of the structure of Al-saturated chlorite from metamorphosed rocks
- XANES study of the oxidation state of Cr in lower mantle phases: Periclase and magnesium silicate perovskite
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