Amorphous Mineral Colloids of Soils of the Pacific Region and Adjacent Areas'

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 investigator