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Spectroscopic standards for four- and fivefold-coordinated Fe^(2+) in oxygen-based minerals

Rossman, George R. and Taran, Michael N. (2001) Spectroscopic standards for four- and fivefold-coordinated Fe^(2+) in oxygen-based minerals. American Mineralogist, 86 (7-8). pp. 896-906. ISSN 0003-004X.

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Optical spectra are presented for seven oxygen based, four-coordinated Fe^(2+) bearing minerals, eudialyte, gehlenite, genthelvite, gillespite, pellyite, spinel, and staurolite, and two five-coordinated Fe^(2+) minerals, grandidierite and joaquinite. Broad, intense spin-allowed dd bands of tetrahedrally coordinated Fe^(2+), originating from the ^5E → ^5T_2 transition, appear in the spectral range 3000–7000 cm^(−1). In the spectra of gillespite and eudialyte, minerals with square-planar coordination, the bands shift to higher energies, appearing in the range 7000–20 000 cm^(−1). The amount of band splitting depends mainly on the distortion of the ligands surrounding four-coordinated Fe^(2+). Splitting and distortion are minimal for spinel with a regular tetrahedral site, and maximal for eudialyte and gillespite. For the minerals in four-coordination, the barycenter of the split bands correlates with the sum of the bond-length and edge-length distortion parameters if the square planer sites are excluded from the correlation. Molar absorption coefficients (ε) of the spin-allowed tetrahedral Fe^(2+) bands range from ~20 cm^(−1)·L·mol^(−1) to ~90 cm^(−1)·L·mol^(−1). For eudialyte and gillespite, due to the centrosymmetric character of the ligand environment, the ε values ranges from about 0.5–10 cm^(−1)·L·mol^(−1). For grandidierite and joaquinite, five-coordination causes spectra that resemble those of Fe^(2+) in highly distorted octahedral sites. The number of bands suggests, however, that the electronic level scheme of five-coordinated Fe^(2+) in grandidierite significantly differs from that of Fe^(2+) in octahedral coordination.

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Rossman, George R.0000-0002-4571-6884
Additional Information:© 2001 American Mineralogist. Manuscript received September 11, 2000. Manuscript accepted March 29, 2001. Paper handled by Celia Merzbacher. Support for this project was provided by National Science Foundation (U.S.A.) grant EAR-9804871 as part of the program for eastern European collaboration. We thank Ray Joesten for providing the analyzed gehlenite sample, Buzz Gray for the joaquinite, and Pat Meagher and Lee Groat for providing the pellyite samples.
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Issue or Number:7-8
Record Number:CaltechAUTHORS:20130417-101420480
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Official Citation:George R. Rossman and Michael N. Taran Spectroscopic standards for four- and fivefold-coordinated Fe2+ in oxygen-based minerals American Mineralogist, July-August, v. 86, p. 896-903
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:37983
Deposited By: Ruth Sustaita
Deposited On:17 Apr 2013 19:03
Last Modified:03 Oct 2019 04:53

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