IN the course of their studies on soil allophane Yoshinaga and Aomine (1962a, b) have noted that certain Ando soils contain, in addition to crystalline clay minerals and free sesquioxides, two different mineral colloids. One of these, which was completely amorphous to X-rays, was called allophane; the other showed some degree of order and was termed imogolite—after Imogo, a brownish yellow volcanic ash soil in the Kuma basin in the Kumamoto Prefecture of Japan. They observed that after deferration of the soil, allophane dispersed in both acidic and alkaline solutions, whereas imogolite dispersed in acid and flocculated in alkali. On electron micrographs imogolite appeared as thread-like particles several μm long and 100 to 200 Å wide.
A mineral component showing similar features was later found in macroscopic gel films filling the interstices of weathered pumice grains (Miyauchi and Aomine, 1966) and in soil clays derived from volcanic ash (Aomine and Miyauchi, 1965; Kawasaki and Aomine, 1966). Early observations were confined to Japanese volcanic ash soils, but imogolite has since been identified in pumice tuff soils of Western Germany (Jaritz, 1967), volcanic ash soils of Papua (Greenland et al., 1969), and Ando soils of Chile (Besoain, 1969).