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Weathering of biotite to vermiculite in Quaternary lahars from Monti Ernici, Central Italy

Published online by Cambridge University Press:  09 July 2018

A. Pozzuoli
Affiliation:
Dipartimento di Geofisica e Vulcanologia, Universitá degli Studi di napoli Federico II, Largo S. Marcellino 10, 80138 Napoli, Italia
E. Vila
Affiliation:
Instituto de Ciencia de Materiales, Sede D, CSIC, Serrano 113, 28006 Madrid, España
E. Franco
Affiliation:
Dipartimento di Scienze della Terra, Università degli Studi di Napoli Federico II, Largo S. Marcellino 10, 80138 Napoli, Italia
A. Ruiz-Amil
Affiliation:
Instituto de Ciencia de Materiales, Sede D, CSIC, Serrano 113, 28006 Madrid, España
C. De La Calle
Affiliation:
Laboratoire de Réactivité de Surface et Structure, URA 1106—CNRS, Université Pierre et Marie Curie, 4 place Jussieu, 75252 Paris Cedex 5, France

Abstract

The weathering of biotite in Quaternary lahars from Monti Ernici (Central Italy) via interstratification stages has been studied by X-ray diffraction of both the interstratified minerals and the initial (biotite) and final (vermiculite) end-members. The structure of the biotite and vermiculite is described by means of monodimensional Fourier series. The interstratified phases have been studied using the INTER program which permits an analysis of two interstratified components by Fourier transform methods. It is shown that in the alteration range for biotite to vermiculite even small samples have different spatial concentrations of biotite, vermiculite and an intermediate biotite-vermiculite-type phase. Hydrobiotite and a rare biotite-hydrobiotite with a tendency to regularity have also been documented. Chemically, the process involves considerable oxidation of Fe2+ and the removal of most of the elements, corresponding to a 34% loss in matter. The sequence of the element losses is: K+ > Fe2+ > F > Mn2+ > Si4+ > Mg2+ > Al3+ > Ti4+. There are also some gains in the order: H+ > Ca2+ > Fe3+ > Na+.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1992

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