The aluminum concentration of muscovite is relatively high among the primary
minerals. The EDX spectrum-mimic graphs, Fig. 2.10d–f, show the number of
cations for the maximum, intermediate, and minimum Al members, respectively,
from among 70 muscovites, phengites, and other potassic white micas per 12 (O,
OH, F) or 22 anions (Fleet 2003). The number of Al ions in Fig. 2.10d, e is close to
that of Si. According to the ideal chemical formula for muscovite (Table 2.1), the
number of Al atoms is the same as the number of Si atoms. In phengite, a portion of
the Al at the octahedral sites is replaced by Mg
2+ . The minimum Al member,
Fig. 2.10f, is celadonite, in which isomorphous substitution at the octahedral sites
is small and the octahedral sites are occupied by Fe
3+ and Mg
2+ . The powder XRD
pattern, Fig. 2.10g, is close to the reference pattern for muscovite, Fig. 2.10h.
Biotite
The biotite series comprises trioctahedral micas with compositions between, or close
to, the phlogopite–annite and eastonite–siderophyllite joins, and also includes
tetraferriphlogopite and tetraferriannite because biotite often contains small amounts
of Fe
3+ in its tetrahedral sites (Fleet 2003). Figure 2.11 shows an example of a
relatively un-weathered biotite particle from a mudflow deposit of Mt. Pinatubo,
Philippines (Fig. 2.7), although biotite particles are not particularly abundant in the
mudflow deposit. The shape of the particle is hexagonal and platy. The EDX
Fig. 2.9 Granitic soil in Singun-ri, the Republic of Korea. (a) Landscape, (b) soil profile and (c)
2–0.2 mm fraction of the soil. The 2–0.2 mm fraction of the C horizon (indicated by an arrow in (b),
100–125+ cm from the surface) includes feldspar, quartz, white mica, weathered biotite, and other
minerals
22
2 Primary Minerals
minerals. The EDX spectrum-mimic graphs, Fig. 2.10d–f, show the number of
cations for the maximum, intermediate, and minimum Al members, respectively,
from among 70 muscovites, phengites, and other potassic white micas per 12 (O,
OH, F) or 22 anions (Fleet 2003). The number of Al ions in Fig. 2.10d, e is close to
that of Si. According to the ideal chemical formula for muscovite (Table 2.1), the
number of Al atoms is the same as the number of Si atoms. In phengite, a portion of
the Al at the octahedral sites is replaced by Mg
2+ . The minimum Al member,
Fig. 2.10f, is celadonite, in which isomorphous substitution at the octahedral sites
is small and the octahedral sites are occupied by Fe
3+ and Mg
2+ . The powder XRD
pattern, Fig. 2.10g, is close to the reference pattern for muscovite, Fig. 2.10h.
Biotite
The biotite series comprises trioctahedral micas with compositions between, or close
to, the phlogopite–annite and eastonite–siderophyllite joins, and also includes
tetraferriphlogopite and tetraferriannite because biotite often contains small amounts
of Fe
3+ in its tetrahedral sites (Fleet 2003). Figure 2.11 shows an example of a
relatively un-weathered biotite particle from a mudflow deposit of Mt. Pinatubo,
Philippines (Fig. 2.7), although biotite particles are not particularly abundant in the
mudflow deposit. The shape of the particle is hexagonal and platy. The EDX
Fig. 2.9 Granitic soil in Singun-ri, the Republic of Korea. (a) Landscape, (b) soil profile and (c)
2–0.2 mm fraction of the soil. The 2–0.2 mm fraction of the C horizon (indicated by an arrow in (b),
100–125+ cm from the surface) includes feldspar, quartz, white mica, weathered biotite, and other
minerals
22
2 Primary Minerals