Amorphous Mineral Colloids of Soils of the 
Pacific Region and Adjacent Areas 1 
Yoshinori Kanehiro 2 and Lynn D. Whittig 3 
The presence of amorphous mineral colloids 
in soils and geologic formations is not as un- 
common as was first believed in the early years 
following the acceptance of the clay mineral 
concept. In the early reports the occurrence of 
amorphous material was associated with only a 
few rare and isolated clay materials. Because 
amorphous colloids are not the major component 
in most soils and their presence may be found 
in relatively low concentrations, if found at all, 
their detection has been difficult. Moreover, 
whereas crystalline clay minerals are relatively 
uniform in composition, the amorphous mate- 
rials exhibit a varying degree of composition 
and poor degree of crystallinity, further adding 
to the difficulty in their identification. Often 
their presence has been suggested only because 
mineral allocations of crystalline materials failed 
to add up to 100 per cent. In recent years im- 
provement in the use of techniques such as 
X-ray diffraction, infrared absorption, electron 
microscopy, and surface area determination, has 
made it possible to make significant progress in 
the study of amorphous colloids. 
Much of the research dealing with amorphous 
mineral colloids in soils has been conducted by 
soil scientists working in the Pacific region or 
in its adjacent areas. The leadership in this field 
definitely belongs to this group of researchers. 
It is the object of this paper to review and 
discuss the contributions of these workers in 
order to obtain a better perspective of this very 
important fraction of soils. These investigators 
1 This paper is based on part of a joint report by 
members of the Clay Mineralogy Work Group of the 
Western Soil and Water Research Committee. Manu- 
script received October 3, I960. 
2 Department of Agronomy and Soil Science, Uni- 
versity of Hawaii, Honolulu. 
3 Department of Soils and Plant Nutrition, Univer- 
sity of California, Davis, California. 
have pointed out that the amorphous consti- 
tuents make up a sizeable fraction in many soils 
occurring in Hawaii, Japan, New Zealand, Ore- 
gon, and other Pacific areas. These amorphous 
mineral colloids play a prominent role in soil 
formation and also impart certain distinctive 
and unique properties to the soil. Thus, a re- 
view of this nature appears justified. 
NOMENCLATURE OF AMORPHOUS COLLOIDS 
The isolation and description of amorphous 
colloids have been difficult because of the great 
variability in materials. Moreover, early sam- 
ples classified as "amorphous” were actually 
found to be finely crystalline with modern X-ray 
diffraction methods. Stromeyer and Hausmann 
first used the name allophane to describe amor- 
phous material lining cavities in marl in 1816. 
Since that time many related materials have 
been called allophane and this term has become 
associated with amorphous constituents of clay. 
Ross and Kerr (1934) described allophane as 
essentially an amorphous solid solution of silica, 
alumina, and water having no definite atomic 
structure, and they applied the term allophane 
to a great number of amorphous clay materials 
regardless of their composition. They studied 
five specimens of allophane, all essentially hy- 
drous aluminum silicates, and found that SiO L > 
ranged from 25 to 34 per cent, AI 0 O 3 from 30 
to 36 per cent, and H 2 0 from 31 to 38 per 
cent. The New Zealand workers (Fieldes et al., 
1952, 1954; Birrell and Gradwell, 1956) have 
used the term amorphous colloidal hydrous ox- 
ides apart from the term allophane in their 
description of amorphous clays. With allophane, 
which is considered to be one of the most im- 
portant amorphous minerals, Fieldes (1955, 
1956) has preferred to recognize three distinct 
477 
