Andisols under semi-dry climates and in the lower horizons of Andisols under humid
climate. Figure 3.6 shows an example of a halloysite-containing, partially weathered
volcanic ash in the lower horizon (2C2) of a soil in Aizu, Japan. A possible reason
for the halloysite formation from volcanic ash is the poor drainage of this area.
The morphological and chemical properties of halloysite are diverse. Halloysite
shows thin platy, curved tubular, and spherically curved properties under TEM
observation (Fig. 3.6b). There are two types of halloysite, halloysite (1.0 nm) and
halloysite (0.7 nm). The values in parentheses indicate their basal spacing. XRD
patterns are effective for distinguishing the two types of halloysite. Glyceration
causes its basal spacing to expand to 1.1 nm, and the basal spacing of halloysite
(1.0 nm) decreases to 0.7 nm with heating at 300
C (Fig. 3.6c). The 0.7 nm basal
spacing of kaolinite and halloysite disappear with heating at 550
C because these
clays are converted to a non-crystalline phase. The CEC of halloysite ranges up to
40 cmol c kg
À1 , and some halloysites show high selectivity for K
+ and NH 4
+
.
Kaolin minerals were described in detail by Dixon (1989). Recently, halloysite
was reviewed by Joussein et al. (2005) and by Churchman et al. (2016).
Fig. 3.5 Kaolinite in soil. (a) Landscape, (b) soil profile with kaolinite-rich soil horizons. A
kaolinite-rich clay fraction was prepared from the Bt2 horizon (b). (c) TEM image, (d) SEM
image, (e) XRD patterns with five treatments (Mg saturation with glyceration, Mg saturation, K
saturation, heating at 300
C after K saturation, and heating at 550
C after K saturation) of the
dithionite–citrate–bicarbonate treated and oriented clay fraction
44
3 Secondary Minerals
climate. Figure 3.6 shows an example of a halloysite-containing, partially weathered
volcanic ash in the lower horizon (2C2) of a soil in Aizu, Japan. A possible reason
for the halloysite formation from volcanic ash is the poor drainage of this area.
The morphological and chemical properties of halloysite are diverse. Halloysite
shows thin platy, curved tubular, and spherically curved properties under TEM
observation (Fig. 3.6b). There are two types of halloysite, halloysite (1.0 nm) and
halloysite (0.7 nm). The values in parentheses indicate their basal spacing. XRD
patterns are effective for distinguishing the two types of halloysite. Glyceration
causes its basal spacing to expand to 1.1 nm, and the basal spacing of halloysite
(1.0 nm) decreases to 0.7 nm with heating at 300
C (Fig. 3.6c). The 0.7 nm basal
spacing of kaolinite and halloysite disappear with heating at 550
C because these
clays are converted to a non-crystalline phase. The CEC of halloysite ranges up to
40 cmol c kg
À1 , and some halloysites show high selectivity for K
+ and NH 4
+
.
Kaolin minerals were described in detail by Dixon (1989). Recently, halloysite
was reviewed by Joussein et al. (2005) and by Churchman et al. (2016).
Fig. 3.5 Kaolinite in soil. (a) Landscape, (b) soil profile with kaolinite-rich soil horizons. A
kaolinite-rich clay fraction was prepared from the Bt2 horizon (b). (c) TEM image, (d) SEM
image, (e) XRD patterns with five treatments (Mg saturation with glyceration, Mg saturation, K
saturation, heating at 300
C after K saturation, and heating at 550
C after K saturation) of the
dithionite–citrate–bicarbonate treated and oriented clay fraction
44
3 Secondary Minerals