Jump to ContentJump to Main Navigation
Show Summary Details
More options …

American Mineralogist

Journal of Earth and Planetary Materials

Ed. by Baker, Don / Xu, Hongwu / Swainson, Ian


IMPACT FACTOR 2017: 2.645

CiteScore 2017: 2.31

SCImago Journal Rank (SJR) 2017: 1.440
Source Normalized Impact per Paper (SNIP) 2017: 1.059

Online
ISSN
1945-3027
See all formats and pricing
More options …
Volume 89, Issue 10

Issues

Behavior of cation vacancy in kenotetrahedral Cr-spinels from Albanian eastern belt ophiolites

Ferdinando Bosi
  • Corresponding author
  • Dipartimento di Scienze della Terra, Università di Roma “La Sapienza„, P.le A.Moro 5, 00185 Roma, Italy
  • Email
  • Other articles by this author:
  • De Gruyter OnlineGoogle Scholar
/ Giovanni B. Andreozzi
  • Dipartimento di Scienze della Terra, Università di Roma “La Sapienza„, P.le A.Moro 5, 00185 Roma, Italy
  • Other articles by this author:
  • De Gruyter OnlineGoogle Scholar
/ Vincenzo Ferrini
  • Dipartimento di Scienze della Terra, Università di Roma “La Sapienza„, P.le A.Moro 5, 00185 Roma, Italy
  • Other articles by this author:
  • De Gruyter OnlineGoogle Scholar
/ Sergio Lucchesi
  • Dipartimento di Scienze della Terra, Università di Roma “La Sapienza„, P.le A.Moro 5, 00185 Roma, Italy
  • Other articles by this author:
  • De Gruyter OnlineGoogle Scholar
Published Online: 2015-03-28 | DOI: https://doi.org/10.2138/am-2004-1003

Abstract

The crystal chemistry of 17 Cr-spinels from the Albanian eastern belt ophiolites was studied by a multi-analytical approach (EMPA, MS, SREF), processing the data with a tested optimization model to obtain site populations. The samples come from the three most important ultramafic massifs of Albania (Tropoja, Bulqiza, and Shebenik), and occur in ultramafic cumulates as well as in ultramafic mantle tectonites, associated with serpentinized olivine. All samples are characterized by Cr ↔ Al and minor Mg ↔ Fe2+ substitutions, and may be classified as magnesiochromite, except one, which is spinel s.s. Cation distributions showed that Cr and Al are ordered in M, and Fe2+ and Mg in the T site. Contents of Fe3+ measured by MS were always higher than those calculated from EMPA, and this non-stoichiometry reveals that the Albanian crystals underwent an increase in fO₂ conditions after mineral formation. Cation vacancies produced by Fe2+ oxidation occur in the T site, and the oxidation mechanism, is described by:

2 TFe2+ + ½ O2 → 2 TFe3+ + O2- + T⃞.

T-O variations show a non-linear regression with TFe2+, and this trend is due to both the cooperative effects of TMg ↔ TFe2+ substitution and TFe2+ oxidation. Cation vacancy in the T site does not impart rigidity to the polyhedron, because it cannot have chemical bonds with ligands: this feature, together with the spinel topology, makes the tetrahedron adopt .soft. behavior. In effect, the T⃞-O distance does not have a single value, but changes according to the population of the M site, as confirmed by comparison with literature data and also by application of the Bond Valence Model.

About the article

Received: 2003-10-20

Accepted: 2004-03-22

Published Online: 2015-03-28

Published in Print: 2004-10-01


Citation Information: American Mineralogist, Volume 89, Issue 10, Pages 1367–1373, ISSN (Online) 1945-3027, ISSN (Print) 0003-004X, DOI: https://doi.org/10.2138/am-2004-1003.

Export Citation

© 2015 by Walter de Gruyter Berlin/Boston.

Comments (0)

Please log in or register to comment.
Log in