Hostname: page-component-586b7cd67f-t7czq Total loading time: 0 Render date: 2024-11-26T09:10:25.875Z Has data issue: false hasContentIssue false
  • English
  • Français

The crystal structure of non-stoichiometric Eu-anorthite: an explanation of the Eu-positive anomaly

Published online by Cambridge University Press:  05 July 2018

Mitsuyoshi Kimata
Mitsuyoshi Kimata*
Affiliation:
Institute of Geoscience, The University of Tsukuba, Ibaraki 305, Japan
Get access Rights & Permissions [Opens in a new window]

Abstract

Synthetic Eu-anorthite of the alkali feldspar structure type has been refined to Rw = 4.7% using 3-D counter diffractometer data and full-matrix least-squares methods. The chemical composition of the feldspar is Eu0.92Al1.76Si2.24O8, based on both occupancy refinement of the Eu atom site and estimation of the Al/Si distribution calculated from the mean T-O bond length. The unit cell parameters are a = 8.373(1), b = 12.959(1), c = 7.124(1) Å, and β = 115.51(1)° and the symmetry is enhanced to C2/m. Mean bond lengths are T(1)-O = 1.677 Å, T(2)-O = 1.668 Å, and Eu-O = 2.721 Å. The average Al/Si distribution over the T(1) and T(2) sites calculated from the mean T-O bond length is in fairly good agreement with an estimate of the Al content from the bond strength calculation; the Al partition is calculated as t1 = 0.47 and t2 = 0.41 respectively. Summing the bond strengths of these Eu and partially disordered Al/Si cations approximates to electrostatic neutrality for the anion content of the feldspar structure, indicating that this synthetic Eu feldspar can be non-stoichiometric, signifying vacancies on the alkali cation site.

Plagioclase and melilite generally show a positive Eu anomaly. A fair insight into the driving force of this anomaly can be afforded by the crystallo-chemical affinities of Eu2+ and Eu3+ cations to the crystal structures of their host minerals; (1) ioinic radius, (2) electrostatic charge balance and (3) tolerance for non-stoichiometry of the crystal structure.

Keywords

feldsparsanorthiteeuropium anomalynon-stoichiometry
Type
Crystallograhy
Information
Mineralogical Magazine , Volume 52 , Issue 365 , April 1988 , pp. 257 - 265
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1988

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

Bettermann, P. and Liebau, F. (1976) Naturwissensch. 63, 480.CrossRefGoogle Scholar
Brown, G.E. (1980) In Orthosilicates (P. H. Ribbe, ed.) Mineral. Soc. Am., Short Course Notes, 5, 275–381.Google Scholar
Brown, I.D. (1981) In Structure and Bonding in Crystals, 2 (M. O'Keefe and A. Navrotsky, eds.). Academic Press, New York, 1-30.Google Scholar
Cameron, M. and Papike, J.J. (1982) In Pyroxenes (C. T. Prewitt, ed.). Mineral. Soc. Am., Short Course Notes, 7, 5-92.Google Scholar
Colville, A.A. and Ribbe, P.H. (1968) Am. Mineral. 53, 25-37.Google Scholar
Doyle, P.A. and Turner, P.S. (1968) Aeta Crystallogr. A24, 390-7.CrossRefGoogle Scholar
Finger, L.W. and Prince, E. (1975) Nat. Bur. Stand. U.S. Tech. Note 854.Google Scholar
Gasparik, T. and Lindsley, D.H. (1980) EOS, 61, 402–3.Google Scholar
Gasperin, M. (1971) Acta Crystallogr. B27, 854-5.CrossRefGoogle Scholar
Grundy, H.D. and Ito, J. (1974) Am. Mineral. 59, 1319-26.Google Scholar
Henderson, P. (1983) In Rare Earth Element Geochemistry (P. Henderson, ed.). Elsevier, Amsterdam, 1-32.Google Scholar
International Tables for X-ray Crystallography (1974) Vol. IV Kynoch Press, Birmingham, England.Google Scholar
Ismatov, A.A. and Gulyamov, B.M. (1976) Izv. Akad. Nauk SSSR, Neorg. Mater. 12, 1065-9.(Russ).Google Scholar
Iwasaki, B. and Kimizuka, N. (1978) Geochem. J. 12, 1-6.CrossRefGoogle Scholar
Johnson, C.K. (1965) Oak Ridge National Laboratory Report ORNL-3794 (second revision, 1970).Google Scholar
Jones, J.B. (1968) Acta Crystallogr. B24, 355-8.CrossRefGoogle Scholar
Kimata, M. (1983) Neues Jahrb. Mineral. Abh. 146, 221-41.Google Scholar
Kimata, M. (1984) Z. Kristallogr. 167, 103-16.CrossRefGoogle Scholar
Kroll, H. and Ribbe, P.H. (1983) In Feldspar Mineralogy (P. H. Ribbe, ed.). Mineral. Soc. Am., Short Course Notes, 2, 2nd ed. 57-99.Google Scholar
Laihunite Research Group (1982) Geochemistry, 1, 105-14.Google Scholar
Lozac'h, A.M., Guittard, M. and Flahaut, J. (1972) C. R. Acad. Sci., Ser. C 275(15), 809-12.(Fr).Google Scholar
McCormick, T.C. (1986) Am. Mineral. 71, 1434-40.Google Scholar
Megaw, H.D. (1970) Acta Crystallogr. B26, 261-5.CrossRefGoogle Scholar
Muller, O. and Roy, R. (1974) The Major Ternary Structure Families. Springer-Verlag, New York, 76-82.CrossRefGoogle Scholar
Nagasawa, H., Blanchard, D.P., Jacobs, J.W., Brannon, J.C., Philpotts, J.A. and Onuma, N. (1977) Geochim. Cosmochim. Acta, 41, 1587-600.CrossRefGoogle Scholar
Neumann, H., Jensen, B.B. and Brunfelt, A.O. (1966) Norsk Geol. Tidsskr. 46, 141-79.Google Scholar
Paques-Ledent, M.T. (1976) Spectrochim Acta, 32A, 383-95.CrossRefGoogle Scholar
Pauling, L. (1960) The Nature of the Chemical Bond, 3rd ed., Cornell University Press, Ithaca, New York.Google Scholar
Ribbe, P.H. (1963) Acta Crystallogr. 16, 426-7.CrossRefGoogle Scholar
Ribbe, P.H. and Gibbs, G.V. (1969) Am. Mineral. 54, 85-94.Google Scholar
Ribbe, P.H. Megaw, H.D. and Taylor, W.H. (1969) Acta Crystallogr. B25, 1503-18.CrossRefGoogle Scholar
Robinson, K., Gibbs, G.V. and Ribbe, P.H. (1971) Science, 172, 567-70.CrossRefGoogle Scholar
Scott, P.W., Critchley, S.R. and Wilkinson, F.C. F. (1986) Mineral. Mag. 50, 141-7.CrossRefGoogle Scholar
Semenov, E.I. (1957) Geochemistry (U.S.S.R.), 735- 48.Google Scholar
Semenov, E.I. (1958)Ibid. 574-86.Google Scholar
Shannon, R.D. (1976) Acta Crystallogr. A32, 751-67.CrossRefGoogle Scholar
Smith, J.V. (1974) Feldspar minerals, vols. 1 and 2. Springer, Berlin.Google Scholar
Smith, J.V. (1983) In Feldspar Mineralogy (P. H. Ribbe, ed.).Google Scholar
Mineral. Soc. Am., Short Courses Notes, 2, 2nd ed. 281-96.Google Scholar
Wuensch, B.J. andPrewitt, C.T. (1965) Z. Kristatlogr. 122, 24-59.CrossRefGoogle Scholar
Zoltai, T. and Buerger, M.J. (1959) Ibid. 111, 129-41.Google Scholar