inside the pumice. At the rim of the pumice, small particles, similar to those seen in
Fig. 4.15e, are found. Several large pores display vacant parts where the penetration
of resin was insufficient. The area shown by the dashed square (Fig. 4.17d) was
further magnified in Fig. 4.18.
Figure 4.18a, b shows element maps for Si and Al, respectively. The intensity of
the cyan color, which indicates Si concentration, is somewhat weak at the rim,
although similar low intensities are found in parts of the interior. The intensity of
the magenta color, which indicates Al concentration, is especially high at the rim, for
example at the site indicated by the white arrow labeled (d) in the SEM image
(Fig. 4.18c), where Si concentration appears low. In contrast, the Si concentration
still appears to be quite high at the site indicated by the white arrow labeled (e) in
Fig. 4.18c. These observations can be confirmed by the EDX spectra (lower right of
Fig. 4.18) of the small parts shown by white arrows labeled (d) and (e) in Fig. 4.18c.
The EDX spectrum (d) shows high Al and low Si concentrations, suggesting the
existence of allophane and imogolite, whereas the EDX spectrum (e) is close to that
of the non-colored volcanic glass (Fig. 4.15e). Thus, consistent with the brownish
color of the pumice in Fig. 4.16b, partial weathering of the pumice particle is shown
by the SEM-EDX analyses. In this example, weathering appears most intensive at
the rim sites of the pumice particle.
Fig. 4.16 Partially weathered pumice. (a) Soil profile, (b) polished section of a weathered pumice
obtained from 2Bw horizon of (a), (c) a landscape around the soil profile
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4 Non-crystalline Inorganic Constituents of Soil