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A new ni-rich stevensite from the ophiolite complex of othrys, central Greece

Christidis Georgios, Ioannis Mitsis

Πλήρης Εγγραφή

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Περίληψη

The first occurrence of Ni-rich stevensite found in the ophiolite complex of Othrys, CentralGreece is described. The stevensite, which develops in cracks in a host serpentinite, formed at the expenseof serpentine. Two varieties of stevensite have been described: a Mg-rich, Ni-poorer variety with 0.41.2octahedral Ni atoms per half formula unit (p.h.f.u.) and a Ni-rich variety with >2 Ni atoms p.h.f.u. Thelayer charge in both varieties is 0.24 p.h.f.u.. Stevensite layers are completely separated when dispersedin dilute polyvinylpyrrolidone (PVP) solutions and begin to convert to talc after heating at 250ºC for90 min. Total conversion to talc is observed at 550ºC. Formation of Ni-rich stevensite took place atambient temperature during supergene processes. The scarcity of Ni-rich stevensite occurrences in natureis 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 newexperimental protocol is proposed for the determination of Ni-rich stevensite, based on a combination ofXRD after solvation with various organic liquids and subsequent heating at 750ºC.

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