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Oxidation Experiment of Natural Megacrystal Clinopyroxene: Implications for Assignment of Mössbauer Spectra
Author(s) -
Xiachen ZHI,
Peng CHEN,
Chengzhong LIN,
Shuqing CHEN,
Guilan ZHANG,
Yuzhi LI,
Lei LIN
Publication year - 2001
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/j.1755-6724.2001.tb00506.x
Subject(s) - mineral redox buffer , mössbauer spectroscopy , chemistry , analytical chemistry (journal) , lattice constant , fugacity , spectral line , mössbauer effect , crystallography , oxygen , diffraction , mineralogy , physics , organic chemistry , chromatography , astronomy , optics
The Mössbauer spectra of natural megacrystal clinopyroxene are usually fitted by 4 sets of symmetric doublets, A‐A', B‐B', C‐C' and D‐D', respectively, in terms of increasing Qs value in literature. But the assignments of those doublets are quite different, except the D‐D' doublet assigned to Fe 3+ at the lattice site M***1 in previous papers. Particularly, the assignment and interpretation of the C‐C' doublet are diverse. The oxidation experiments of natural megacrystal clinopyroxene collected from the Hannuoba basalt, North China, were performed under controlled conditions of temperature at 1000°C and oxygen fugacity of FMQ buffer in 1, 2, ***3 and 5 days respectively. The oxidized samples were then measured by X‐ray diffraction spectrometry and Mössbauer spectrometry. The oxidation of clinopyroxene is characterized by Fe 2+ → Fe 3+ at M1 under the subsolidus conditions, which is consistent with the increase of the area of the D‐D' doublet when the heating time increases. Accordingly, the area of the A‐A' and B‐B' doublets decreases with the increasing heating time. However, the area of C‐C' keeps almost constant. Therefore, the 4 sets of doublets can be assigned correctly as follows: A‐A' doublet to Fe +2 at M1, B‐B' Fe 2+ at M1, C‐C' Fe 2+ at M2, and D‐D' Fe 3+ at M1. The M1 site splitting is due to the NNN (Next Nearest Neighbour) effect of the M2 site. The amount of Fe 3+ at the tetrohedral site of megacrystal clinopyroxene is negligible according to this study.