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

Abstract

A B S T R A C T: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 Fe 2+ and the removal of most of the elements, corresponding to a 34% loss in matter.

Morphological and Chemical Features of Bioweathered Granitic Biotite Induced by Lichen Activity

“…These authors found out that even small samples are normally characterized by different spatial concentrations of biotite, vermiculite and an intermediate interstratified phase in dependency to the alteration grade. Our results for the geochemical mass balance (Table 2) as element losses or gains and total loss of mass of the bioweathered biotite zone were in good agreement with data obtained by Pozzuoli et al (1994) and suggest the transformation biotite to scarcely altered biotite with a biotite-vermiculite intermediate interstratified phase. However, additional work remains to be done to confirm the occurrence of this mineralogical transformation of biotites in the lichen-mineral interface.…”

“…The geochemical mass balance data showed in Table 2 indicates that loss of Fe as total Fe was observed. The application of microprobe analysis does not perrnit determination of the valence of the Fe cations, but according to Pozzuoli et al (1994) more intensive decreases in Fe 2+ than gains in Fe 3 § during the first stage of natural weathered biotite can be suspected. Moreover, an increase in Ca 2 § and Na § in the interlaminar spacing was observed.…”

“…The transformation of mica into vermiculite has been observed in laboratory experiments by Weed et al (1969) as a result of K exchange by cations present in nutrient solution, and soil fungi shifted the equilibrium in this reaction by absorption of K + cations. According to recent studies carried out by Pozzuoli et al (1994), natural weathering of biotite to vermiculite occurred in a localized and heterogeneous way. These authors found out that even small samples are normally characterized by different spatial concentrations of biotite, vermiculite and an intermediate interstratified phase in dependency to the alteration grade.…”

“…The number of ions contained within a single unit cell network based on 22 O atoms has also been transformed into the weights of the corresponding elements and the loss, or gain, of each element, and the total loss of matter has thus been obtained (Lineares et al 1987;Pozzuoli et al 1994).…”

Interaction of Vermiculite with Aliphatic Amides (Formamide, Acetamide and Propionamide): Formation and Study of Interstratified Phases in the Transformation of Mg- to NH4-Vermiculite

“…The program allows diffraction effects to be calculated from given mixtures (XRD Intensity Function) and compared with experimentally recorded diffraction curves. This program was also used to calculate the distribution function of interlayer distances, W(R), by the direct Fourier transform method (Martfn de Vidales et al 1990;Arag6n de la Cruz et al 1992;Pozzuoli et al 1992;Ruiz-Amil et al 1992;Ruiz-Amil et al 1993). …”