Hostname: page-component-78c5997874-dh8gc Total loading time: 0 Render date: 2024-11-05T15:39:19.001Z Has data issue: false hasContentIssue false
  • English
  • Français

Structural interpretation of polarized absorption spectra of the Al-Fe-Mn-Cr epidotes

Published online by Cambridge University Press:  14 March 2018

R. G. Burns  and
R. G. J. Strens
R. G. Burns
Affiliation:
Department of Mineralogy and Petrology, Downing Place, Cambridge
R. G. J. Strens
Affiliation:
Department of Mineralogy and Petrology, Downing Place, Cambridge
Get access Rights & Permissions [Opens in a new window]

Summary

Measurements have been made of the magnetic susceptibility and of the polarized absorption spectra of epidotes of the Al-Fe, Al-Fe-Mn, and Al-Cr series. Magnetic susceptibility measurements at room temperature by the Guoy method indicate that Fe3+, Mn3+, and Cr3+ are in ‘high-spin’ electronic states in the epidote structure, and the electronic transitions observed in the absorption spectra have been assigned on this basis. The polarized spectra, measured over the range 4000 to 22 000 Å by a polarizing microscope using a universal stage technique, showed each epidote group to be distinctly pleochroic. This pleochroism correlates with the presence of ions in distorted coordination sites.

Extinction coefficients of Fe3+ in epidote are higher than those for other Fe (III) compounds, indicating that Fe3+ ions occupy the non-centrosymmetric (Al, Fe) site. The low value (13200 cm−1 at 0·155 Fe3+ and 12700 cm−1 at 0·915 Fe3+) of the crystal-field splitting parameter, Δ, implies that the site is easily expanded to accommodate ions larger than Al3+ There is also evidence that increasing Fe3+ content causes distortion of the (Al,Fe)O6 octahedron, suggesting a possible mechanism for the zoisite ⇌ clinozoisite transition.

The spectra of Al-Mu-Fe epidotes have been interpreted in terms of intense contributions from Mn3+ ions in the non-centrosymmetric (Al, Fe) site, and weak contributions from Mn3+ ions in the centrosymmetrie AlOH site. Values of Δ vary from 13730 cm−1 (0·082 Mn3+) to 13400 cm−1 (0·747 Mn3+). Both (Al, Fc) and AlOH sites have strong tetragonal distortions (c/a ~ 0·95), leading to the observed large Jahn-Teller splitting of 12000 cm−1.

The Al-Cr epidote spectra show weak absorption bands, attributed to Cr3+ ions in a centrosymmetric site of approximately orthorhombic symmetry (i.e. the AlO site). The value of Δ is about 16300 cm−1.

Review of all available data on the distribution of Fe3+, Mn3+, and Cr3+ between the sites gives the following site preferences: Fe3+, Al > AlO > AlOH; Mn3+, Al ≥ AlOH ≫ AlO ; Cr3+, AlO ≫ Al, AlOH.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 36 , Issue 278 , June 1967 , pp. 204 - 226
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1967

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Barrow, (G. M.), 1960. Introduction to Molecular Spectroscopy. McGraw-Hill Book Co., New York.Google Scholar
[Belov, (N. V.) and Rumanova, (I. M.)] 1954. (Proc. Inst. Cryst. Acad. Sci. Ussr), vol. 9, p. 103.Google Scholar
Burns, (R. G.), 1965. Ph.D. Diss., Univ. California, Berkeley, California.Google Scholar
Burns, (R. G.), 1966. Journ. Sci. Instr., vol. 43, p. 58.Google Scholar
Burns, (R. G.), Clark, (R. H,), and Fyfe, (W. S.), 1964. Chemistry of the Earth's Crust. Proc. Vernadsky Cent. Symp., vol. 2, p. 88.Google Scholar
Burns, (R. G.) and Fyfe, (W. S.), 1967. in Abelson, (P.), ed., Researches in Geochemistry (J. Wiley and Sons, New York), second edn, (in press).Google Scholar
Cotton, (F. A.), 1963. Chemical Applications of Group Theory. Interscience Publ., New York.Google Scholar
Dingle, (R.), 1965. Inorg. Chem., vol. 4, p. 1287.Google Scholar
Dunn, (T. M.), 1960. in Lewis, (J.) and Wilkins, (R. G.), ed., Modern Coordination Chemistry (Interscience Publ., New York), p. 229.Google Scholar
Ferguson, (R. B.), Traill, (R. d.), and Taylor, (W. H.), 1958. Acta Cryst., vol. 11, p. 331.CrossRefGoogle Scholar
Gottardi, (G.), 1954. Periodico Min., vol. 23, p. 245.Google Scholar
[Grum-Grzhimailo, (S. V.), Brilliantov, (N. A.), Sviridov, (D. T.), and Sviridova, (R. K.)] 1963. vol. 14, p. 22. (Optics and Spectr., vol. 14, p. 118).Google Scholar
Hartmann, (H.) and Sciläfer, (H. L.), 1951. Zeitschr. Naturforsch., vol. 6, p. 760.CrossRefGoogle Scholar
Ito, (T.), 1950. X-ray Studies on Polymorphism. Maruzen Co., Tokyo.Google Scholar
Ito, (T.), Morimoto, (N.), and Sadanaga, (R.), 1954. Acta Cryst., vol. 7, p. 53.CrossRefGoogle Scholar
Jørgesen, (C. K.), 1954. Acta Chem. Scand., vol. 8, p. 1502.CrossRefGoogle Scholar
Jørgesen, (C. K.), 1962. Absorption Spectra and Chemical Bonding in Complexes (Pergamon Press, London).Google Scholar
Lewis, (J.) and Figgis, (B. N.), 1960. in Lewis, (J.) and Wilkins, (R. G.), ed., Modern Coordination Chemistry (Interscience Publ., New York), p. 400.Google Scholar
McClure, (D. S.), 1962. Journ. Chem. Phys., vol. 36, p. 2757.Google Scholar
Neuhaus, (A.), 1960. Zeitschr. Krist., vol. 113, p. 195.Google Scholar
Newnham, (R. E.) and De Haan, (Y. M.), 1962. Zeitschr. Krist., vol. 117, p. 235.Google Scholar
Orgel, (L. E.), 1955. Journ. Chem. Phys., vol. 23, p. 1004.Google Scholar
Orgel, (L. E.), 1960. An Introduction to Transition-Metal Chemistry: Ligand-Field Theory (Methueu and Co., London).Google Scholar
Strens, (R. G. J.), 1965. Min. Mag., vol. 35, p. 547.Google Scholar
Strens, (R. G. J.), 1966. Ibid, vol. 35, p. 928.Google Scholar
Wickersheim, (K. A.) and Lefever, (R. A.), 1962. Journ. Chem. Phys., vol. 36, p. 844.CrossRefGoogle Scholar