Fe{sup 3+} distribution in oxidized olivine: A synchrotron micro-XANES study

Journal Article · Sun Nov 01 04:00:00 EST 1998 · American Mineralogist

DOI:https://doi.org/10.2138/am-1998-11-1227· OSTI ID:343761

Dyar, M D ^[1]; Delaney, J S ^[2]; Sutton, S R ^[3]; Schaffer, M W ^[4]

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1. Mount Holyoke Coll., South Hadley, MA (United States). Dept. of Geography and Geology
2. Rutgers Univ., Piscataway, NJ (United States). Dept. of Geological Sciences
3. Univ. of Chicago, IL (United States)
4. Yale Univ., New Haven, CT (United States). Dept. of Geology and Geophysics

Synchrotron micro-XANES spectroscopy (SmX) is used to examine the amount and distribution of Fe{sup 2+} and Fe{sup 3+} in five samples of fayalite previously studied by Moessbauer spectroscopy. Rockport fayalite is homogeneous and the Fe in it is completely reduced. Olivine from Qianan is almost completely oxidized, and probably contains finely intergrown silica, laihunite, and hematite with hematite predominating. Pantelleria olivine has an oxidized rim around a reduced core, suggesting either a post-crystallization reaction with fayalite and oxygen going to laihunite and hematite or a change in prevailing oxidation during growth. The texture of olivine from the Mourne Mountains suggests exsolution from a fayalite-laihunite solid solution, based on the substitution of three Fe{sup 3+} atoms for two Fe{sup 3+} and one vacancy, that was stable at high temperature. Laihunite from the type locality (Lai-He village) shows 1--3 {micro}m mottling between light and dark areas in backscatter images, but these areas cannot correspond to pure fayalite and laihunite exsolution because the bulk Fe{sup 3+}/{Sigma}Fe of such a combination would not correspond to the SmX value of 67% Fe{sup 3+}. Rather, the texture observed in backscatter is interpreted to represent alternating areas of magnetite-rich and laihunite-rich compositions with a similar (i.e., 67% Fe{sup 3+}/{Sigma}Fe) extent of oxidation.

• Research Organization: Brookhaven National Laboratory (BNL), Upton, NY
• Sponsoring Organization: USDOE, Washington, DC (United States); National Aeronautics and Space Administration, Washington, DC (United States); National Science Foundation, Washington, DC (United States)
• DOE Contract Number: FG02-92ER14244; AC02-76CH00016
• OSTI ID: 343761
• Journal Information: American Mineralogist, Journal Name: American Mineralogist Journal Issue: 11-12Pt1 Vol. 83; ISSN AMMIAY; ISSN 0003-004X
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
DISTRIBUTION
IRON
MINERALOGY
OLIVINE
ORIGIN
OXIDATION