Amorphous Mineral Colloids — Kanehiro and WHITTIG 
479 
low bulk density, a high organic carbon con- 
tent, and low base saturation. These properties 
are attributed to the preponderance of allo- 
phane. The Ando soils and related types are 
found associated with the Pacific ring of vol- 
canic activity. These Japanese workers have 
found that the fine clay fraction of the Ando 
soils is characterized by being amorphous to 
X-rays and possesses medium-to-high cation ex- 
change capacities and high phosphate- and 
ethylene glycol-retention values. 
The New Zealanders have also worked ex- 
tensively on the identification of amorphous con- 
stituents. In 1952 Birrell and Fieldes (1952) 
and Birrell (1952) identified the presence of 
amorphous material, principally allophane, in 
soils derived from rhyolitic and andesitic ash. 
The allophane was found to be present mainly 
in the clay fraction although it was inferred 
that it was present to some extent in the silt 
fraction. These soils were characterized by a 
high water-holding capacity, high shrinkage, and 
irreversible drying, characteristics that are strik- 
ingly common to many other Pacific region soils 
dominated by allophane. Birrell ( 1952 ) also 
pointed out that these soils had a waxy appear- 
ance and were greasy to the feel, yet they were 
not unusually sticky. He further noted that as- 
sociated with nonreversible drying, liquid and 
plastic limit values were much greater for un- 
dried soils than for dried soils. 
Later reports, especially by Fieldes and his 
co-workers ( 1955, 1956, 1957, 1955), have con- 
firmed that allophane and other amorphous con- 
stituents dominate many New Zealand soils de- 
rived from volcanic ash and, in some cases, 
basaltic parent materials. These workers utilized 
electron microscopy, differential thermal analy- 
sis, and infrared absorption extensively in iden- 
tifying the presence of amorphous constituents. 
PEDOGENIC SIGNIFICANCE OF 
AMORPHOUS COLLOIDS 
Ross and Kerr (1934) described allophane 
as an amorphous hydrous aluminosilicate having 
no definite chemical composition and that it is 
commonly associated with halloysite. They were 
careful to point out that it is not a microscopic 
mixture of amorphous silica and alumina. Kerr 
(1951) offered confirmatory evidence by ab- 
sorption spectra that allophane is not a mixture 
of alumina and silica. 
Tamura et al. (1953) assigned allophane to 
weathering stage 1 1 or the gibbsite stage in the 
weathering sequence of clay-size minerals as 
presented by Jackson et al. ( 1948). They noted 
that the trend for increased gibbsite with in- 
creased rainfall is very marked in passing from 
the low humic latosols to the hydrol humic 
latosols. With this increase in gibbsite is an 
associated increase in allophane. 
A mechanism for the transition of alumina 
and silica through allophane to kaolin was pro- 
posed by Tamura and Jackson (1953). The 
steps are as follows: (1) amorphous hydrous 
alumina crystallizes to a gibbsite structure; ( 2 ) 
with partial dehydration, hydroxyls in the gibb- 
site octahedra are replaced by oxygens of the 
silica tetrahedra; ( 3 ) this process occurs in the 
presence of silica solutions and continues 
through entrance of silica between gibbsite 
sheets, resulting in a cross-linking of silicated 
octahedral sheets of alumina which corresponds 
to allophane; (4) kaolinite is formed from 
allophane on completion of unidirectional bond- 
ing through alternate wetting and drying in an 
acid medium where enough silica is available. 
The stable, nonreactive form of allophane re- 
ported by Whittig (1954) as a constituent of 
some humic ferruginous latosols of Hawaii was 
considered to be a weathering product of hal- 
loysite. Electron micrographs of clay fractions 
of these soils revealed a transition from well- 
developed halloysite rod structures to spherical, 
X-amorphous allophane particles. It was sug- 
gested that partial removal of silica from the 
rigid halloysite rods by leaching allowed the 
rods to curl up in a direction perpendicular to 
their original curvation. Allophane formed in 
this way possessed properties quite different from 
those of the more labile allophane described by 
Tamura and Jackson ( 1953) and would occupy 
a lower position in the weathering sequence of 
Jackson et al. (1948). 
More recently Bates (I960) suggested that 
the development of allophane is a logical stage 
in the weathering of certain Hawaiian volcanic 
ash and also in the matrix of rock. In other 
cases, he indicated that allophane is an inter- 
