Fjölrit RALA - 15.06.2004, Blaðsíða 81

Such behaviour is associated with the presence of exchangeable aluminum which accumulates
in the lower part of the profile (horizons BC2 and C). The differences in the values of the
chemical parameters of the two profiles EUROl and EUR02 can also be related to differences
in soil management; in fact the EUROl profile show a lower content of organic matter and
CEC. The profile EUR02 has very high values of CEC that was not correlated to the presence
of organic matter. The micromorphological analysis has shown the rare presence of clay
coatings in the C horizons along with pumice having different degree of weathering. The
chemical analysis obtained by SEM - EDS on the same sections has shown that the silicon has
accumulated in the extemal parts of the pumice; such areas appeared optically isotropic to the
OM while aluminum has a very different distribution from the silicon. In addition other
element mapping of the pumice in the thin sections have shown in prevalence similar
distribution of alkaline cations, indicative of moderate weathering (Fig.l). Mineralogical
composition of the clays has shown the presence of halloysite (hydrated form) with a peak at
1 nm and meta-halloysite with a peak at 0.72 nm. In the clayey fraction zeolitic minerals
(mainly analcime and philippsite) have also been observed, in the deepest horizons ( (BCl,
BC2 e C1 of the EUR02 profile), while in the top soil zeolites clearly decrease(Ming et al.,
1989). In the sand fraction biotite, leucite, sanidine have been observed along with minor
content of phillipsite ed analcime. The presence of such mineral related with higher values of
CEC in the EUR02 profxle results of particular interest, to understand the weathering of the
zeolites mineral and their influence on the specific chemical characteristics of the volcanic
soil in the Flegrei Fields district.
References
Ming D. W., and Mumpton F. A. (1989). Zeolites in Soils. In Minerals in Soil Environments
(2nd Edition) - SSSA Book Series, no.l., Ed. J. B. Dixon e S.B. Weed., 873-911.
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