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Clays and Clay Minerals; December 2006; v. 54; no. 6; p. 653-666; DOI: 10.1346/CCMN.2006.0540601
© 2006 Clay Minerals Society
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A NEW Ni-RICH STEVENSITE FROM THE OPHIOLITE COMPLEX OF OTHRYS, CENTRAL GREECE

George E. Christidis1,* and Ioannis Mitsis2

1 Technical University of Crete, Department of Mineral Resources Engineering, 73100, Chania, Greece
2 Section of Geochemistry and Economic Geology, Department of Geology, University of Athens, Panepistimioupolis, Ano Ilisia 15784, Greece

* E-mail address of corresponding author: christid{at}mred.tuc.gr

The first occurrence of Ni-rich stevensite found in the ophiolite complex of Othrys, Central Greece is described. The stevensite, which develops in cracks in a host serpentinite, formed at the expense of serpentine. Two varieties of stevensite have been described: a Mg-rich, Ni-poorer variety with 0.4–1.2 octahedral Ni atoms per half formula unit (p.h.f.u.) and a Ni-rich variety with >2 Ni atoms p.h.f.u. The layer charge in both varieties is –0.24 p.h.f.u.. Stevensite layers are completely separated when dispersed in dilute polyvinylpyrrolidone (PVP) solutions and begin to convert to talc after heating at 250°C for 90 min. Total conversion to talc is observed at 550°C. Formation of Ni-rich stevensite took place at ambient temperature during supergene processes. The scarcity of Ni-rich stevensite occurrences in nature is attributed to the metastability of smectite and to the analytical procedures used in previous studies. Stevensite is considered a phase containing domains with variable numbers of octahedral vacancies. A new experimental protocol is proposed for the determination of Ni-rich stevensite, based on a combination of XRD after solvation with various organic liquids and subsequent heating at 750°C.

Key Words: Greece • Metastability • Ni-rich Stevensite • Octahedral Vacancy • Othrys Ophiolite Complex • PVP • Serpentine • Supergene Alteration • Talc • XRD






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